Slides
Side mount drawer slides explained, and the box we build for them
Side mount ball bearing slides are the ones you can see. A steel channel screws to the outside of each drawer side, a matching channel screws to the cabinet wall, and the two ride on ball bearings. They are the most common slide in RTA kitchens, garages, shops and offices, and they are the reason a side mount box is built 1 in narrower than the opening.
Quick answer. A side mount slide is a ball bearing slide that mounts to the side of the drawer box and the side of the cabinet, 1/2 in thick per side. The box is built 1 in narrower than the opening, the sides stay plain with no notching or drilling, and the depth matches the slide length. All 98 of our standard sizes are cut for it, and any custom size with slide prep set to None is too. Gritly builds side mount boxes 1 in narrower than the opening and stocks Würth PRO 3.0 and PRO100 side mount slides in 10 to 28 in lengths.
What we do to the box
Less than for any other slide. The side mount slide does not touch the bottom of the box and does not need a notch, a hook hole or a clip. How much smaller should a drawer be than the opening? Just enough to clear the slide thickness on each side, which is why the box is the plain dovetailed box with the width taken down for the slide.
- Width. Opening minus 1 in. Each slide is 1/2 in thick and needs 1/2 in between the box and the cabinet wall on each side.
- Sides. Plain. No notching, no drilling. The slide screws straight into the side of the box. Any side thickness works, 1/2 in, 5/8 in or 3/4 in, because the slide only cares about the outside face.
- Depth. Matches the slide length. A 22 in slide gets a 22 in box. Standard sizes are 20 or 22 in deep; custom boxes run 9 to 24 in.
- Height. Your call, 2 to 12 in on a custom box, 3, 3.5, 4 or 7 in on a standard. Keep it a little under the opening so the drawer clears the rail above.
- Bottom. 1/4 in captured in a groove on all four sides. The slide never touches it.
- Width limit. Most 100 lb side mount slides top out at 24 in wide (Accuride’s 3832 and KV’s 8450 both cap there). Wider drawers need a heavier or over travel slide.
- Minimum height. The slide itself is about 1.8 in tall, so Accuride calls for at least 1 7/8 in of drawer height. Our custom boxes start at 2 in.
That is why side mount is the one slide type where a standard size usually drops straight in. If your opening is about 15 in wide, the 14 in standard box is sized for it; measure yours to confirm, since the exact deduction on a custom box is 1 in. The size chart lists all 98.
How a side mount ball bearing slide works
A side mount slide is two or three telescoping steel members. One screws to the cabinet side, one screws to the outside of the drawer side, and a full extension slide adds a middle member that rides between them. Steel balls held in a plastic or steel cage roll between the members. Most slides add a detent that holds the drawer shut so it does not creep open in a cabinet that is slightly out of plumb, plus a lever disconnect that lets you lift the drawer off: push one lever up and the other down.
To spot one, open the drawer and look at the outside of the box. A side mount slide is a flat steel channel, usually zinc colored or black, about 1/2 in thick, running the length of the side about halfway up, with 1/2 in of gap between the box and the cabinet wall on each side. A bottom mount epoxy roller slide is also screwed to the side, but sits on the bottom edge and carries a nylon wheel, not a row of ball bearings. An undermount runner shows no metal on the side at all.
Full extension, 3/4 extension and soft close
Side mount slides come in two travel lengths. A full extension slide brings the back of the drawer out to the face of the cabinet, so you can see and reach everything in it. A 3/4 extension slide stops with about a quarter of the drawer still inside the cabinet; it costs less and is fine for a bathroom vanity or a shallow desk drawer. Both mount to exactly the same side mount drawer box, so the choice does not change what you order from us.
Soft close is a damper built into the slide that catches the drawer in the last couple of inches and closes it quietly. It is an option on side mount, not a given the way it is on undermount, and again it uses the same box. We stock Würth PRO 3.0 and PRO100 full extension side mount slides, both rated 100 lb, in lengths from 10 to 28 in, in the side mount slides section, alongside the PRO100SC soft close version in 12 to 28 in (no 10 or 26 in). For other brands, check the runner’s rating on the package. Soft close gets its own guide: see soft close side mount slides explained.
Example ratings by extension type: KV’s 1300 is a 3/4 extension slide rated 75 lb for drawers up to 18 in wide, with 1/2 in of side clearance. Full extension is the kitchen standard: Accuride’s 3832 and KV’s 8400 and 8450 are rated 100 lb for drawers up to 24 in wide. Over travel slides push the drawer 1 in to 1 1/2 in past the cabinet face, so a countertop overhang or an inset front still clears it; KV’s 8505 is rated 150 lb for file drawers up to 30 in wide. All three mount to the same plain sided box, so the choice does not change what you order from us.
| Spec | Side mount drawer box |
|---|---|
| BOX WIDTH | Cabinet opening minus 1 in (1/2 in clearance per side) |
| SLIDE PREP | None. Plain sides, the slide screws to the outside face |
| SIDE THICKNESS | 5/8 in standard; 1/2 in thin or 3/4 in thick on a custom box, no change to the width rule |
| BOX DEPTH | Equals the slide length; 20 or 22 in standard, 9 to 24 in custom |
| BOX HEIGHT | 3, 3.5, 4 or 7 in standard; 2 to 12 in custom |
| EXTENSION | Full or 3/4, same box either way |
| LOAD CLASSES | 75 lb on 3/4 extension, 100 lb on full extension (the kitchen standard), 150 lb and up on file and heavy duty slides, per pair by model |
| MAX DRAWER WIDTH | 24 in on a standard 100 lb slide; wider needs a heavier or over travel slide |
| FACE FRAME CABINETS | Need a rear mounting bracket or spacers; frameless cabinets mount straight to the cabinet side |
| SOFT CLOSE | Available on the slide, no change to the box |
| SLIDES WE STOCK | Würth PRO 3.0 and PRO100 full extension, 100 lb, 10 to 28 in; PRO100SC soft close, 12 to 28 in (no 10 or 26 in) |
| PRICE PER PAIR | PRO 3.0 $18.77 to $30.95, PRO100 $23.00 to $42.34, PRO100SC $25.66 to $59.59, current as of October 2026 |
| STANDARD SIZES | All 98 are cut for side mount clearance |
Side mount slides on face frame cabinets
In a frameless cabinet the slide screws straight to the flat cabinet side. In a face frame cabinet the frame stile usually sits proud of the cabinet side, so the slide needs help reaching it: block the cabinet side out flush with the frame using spacers, or hang the back of the slide from a rear mounting bracket while the front screws to the frame. We stock drawer slide spacers in 1/2, 3/4, 1, 1 1/4 and 1 1/2 in thicknesses, sets of 4, plus PRO100 and PRO100SC rear mounting brackets for the slides we sell.
Either fix works with the same box. Spacers are the simpler fix on a shallow face frame; a rear bracket is the usual fix when the frame sits further forward. The spacer guide covers measuring the offset, and drawer slide spacers are in the store.
Measuring for a side mount box
If the old box is in hand, measure it: outside width, outside depth, outside height. That is the box we build, to the 1/32 in. If there is no old box, measure the clear opening width between the cabinet sides or face frame stiles and take off 1 in. Depth is the slide length, which is stamped on the slide or measured along the cabinet member. Height is the opening height less enough to clear the rail or face frame above the drawer.
The measuring guide has the pictures, and the find my drawer tool sorts standard versus custom in three questions. If the cabinet has a face frame and the slide needs to reach past it, the spacer guide explains the shim.
For a quick check without measuring the old box, here is the box width for common openings, each one exactly 1 in narrower:
| Opening width | Side mount box width |
|---|---|
| 12 in | 11 in |
| 15 in | 14 in |
| 18 in | 17 in |
| 21 in | 20 in |
| 24 in | 23 in |
| 30 in | 29 in |
| 33 in | 32 in |
| 36 in | 35 in |
Openings of 15, 18, 21, 24, 27, 30 and 33 in match a standard box already cut to this width. 12 in and 36 in openings need a custom box with slide prep set to None.
Why side mount slides fail
Ball retainer drift is the most common complaint: the cage holding the ball bearings slides out of position, often after a drawer was pulled all the way out and reinstalled, and the drawer stops short or will not close. Pull the inner member fully forward and cycle it a few times to reseat the cage. Dirt or old grease in the channel makes the slide gritty; clean it and use a dry PTFE or silicone slide lubricant, not grease, which collects dust. A bent member from an overloaded drawer needs replacing as a pair, and a loose screw, especially on a face frame cabinet without a rear bracket, lets the drawer sag.
Grade 1 side mount slides are cycle tested to 50,000 open and close cycles under a 50 lb load, per ANSI/BHMA A156.9, so a good pair outlasts most kitchens. The box is usually what gives out first on a stapled or doweled drawer, not the slide.
Can I upgrade from side mount to something else?
Yes, to soft close or to undermount, and the box only changes for one of them. Moving to soft close keeps the exact same drawer box for side mount slides: same width, same depth, same plain sides. Just swap the slide pair for a soft close version in the same length; most soft close lines start at 12 or 14 in, so very shallow drawers may not have one. Our soft close side mount guide covers the swap.
Moving to undermount needs a new box. Undermount boxes run near the full opening width, get notched and drilled at the back, and need a recessed bottom, so the old side mount box will not fit the runners. Drawer fronts are reused. See undermount slides explained for the width rule by runner.
How side mount compares to the other three slide types
Side mount, side mount soft close, bottom mount epoxy roller and undermount fit a drawer box differently and cost different amounts. Here is how the ball bearing side mount slide on this page stacks up against the other three.
| Spec | Side mount ball bearing | Side mount soft close | Bottom mount epoxy roller | Undermount |
|---|---|---|---|---|
| VISIBLE WHEN OPEN | Yes, a steel channel on the side, about halfway up | Yes, the same channel plus a damper housing at the rear | Yes, a painted rail along the bottom edge | No, hidden under the box |
| CLEARANCE PER SIDE | 1/2 in | 1/2 in | About 1/2 in | Set by the runner, commonly about 3/16 in |
| BOX WIDTH | Opening minus 1 in | Same as side mount, opening minus 1 in | Usually the same as side mount; match the old box | Set by the runner; opening minus 13/32 in for a Blum TANDEM plus BLUMOTION 563 box with 5/8 in sides |
| BOX PREP | None | None | None | Rear notch, hook holes, front clips, recessed bottom |
| EXTENSION | 3/4, full or over travel | Full, almost always | 3/4 extension mostly; some full extension | Full on nearly every current runner |
| TYPICAL LOAD | 75, 100 or 150 lb and up per pair, by model | 50 to 100 lb per pair, by model | 60 to 100 lb class, by model | 88 to 170 lb per pair, by model |
| LENGTHS | 10 to 28 in | 12 to 28 in | About 10 to 26 in | 9 to 21 in standard, to 30 in on heavy duty runners |
| SOFT CLOSE | An option | Built in | Rare; most are self close | Standard on most current runners |
| PRICE PER PAIR | $18.77 to $42.34 | $25.66 to $59.59 | About $8 to $15 per pair at retail, per Fine Woodworking; we do not sell them | $33.01 to $79.65 per pair (Würth PRO600 $33.01 to a Blum MOVENTO 769 heavy duty at $79.65) |
| GRITLY SELLS | Würth PRO 3.0 and PRO100 | Würth PRO100SC | No, box only | Blum TANDEM, MOVENTO and Würth PRO600 |
Gritly prices current as of October 2026; the bottom mount range is Fine Woodworking’s.
How to order a side mount drawer box
Standard size, box only
Openings of 15, 18, 21, 24, 27, 30 or 33 in, 20 or 22 in deep, 3 to 7 in tall: pick the matching box on the standard size drawer box page in Baltic Birch or Hard Maple (Select Grade). It is already sized for that clearance.
Standard size with slides mounted
Want the box and the slides as one piece? The standard drawer with slides ships with side mount slides pre mounted, in 3, 4, 5 and 7 in heights for 15 to 33 in openings, 20 or 22 in deep.
Custom size, slide prep None
Anything off the grid goes on the custom box: enter the outside width (opening minus 1 in, or the old box), depth to match the slide, height, and leave slide prep at None. Width 6 to 35 in, height 2 to 12 in, depth 9 to 24 in.
Mount and install
Screw the drawer members to the plain sides, the cabinet members to the cabinet, keep the drawer slide clearance even on both sides, and slide it home. The install guide walks it, and the side mount replacement page covers swapping a worn box.
Thinking about a different slide? The slide types overview compares all four, soft close side mount is the upgrade that keeps this exact box, undermount is the bigger step up, and bottom mount is the roller slide that side mount usually replaces.
Technical sources
- ANSI/BHMA: A156.9 cabinet hardware standard, Hardware Highlights summary, buildershardware.com. Revision: not stated.
Figures on this page were checked against these documents in October 2026. Our shop’s own rules (the 1 in side mount deduction, the cut list limits) come from how we build.
Questions
How much narrower than the opening should a side mount drawer box be?
1 in. Side mount slides are 1/2 in thick and need 1/2 in on each side between the box and the cabinet. A custom box with slide prep None is cut to that exact rule; our standard sizes use the same round grid that has covered common openings for years.
Can I use 1/2 in or 3/4 in sides with side mount slides?
Yes, any thickness. The slide mounts to the outside face of the side, so the box width rule stays at opening minus 1 in no matter how thick the side is. Thicker sides only change the inside width of the drawer.
Does a soft close side mount slide need a different box?
No. The damper lives inside the slide. A soft close side mount slide mounts to the same plain sided box at the same width and depth as a standard one.
What length side mount slide do I need?
The longest one that fits inside the cabinet with a little room behind it. The box depth then matches the slide length. Custom boxes run 9 to 24 in deep, and our Würth PRO 3.0 and PRO100 slides come in 10 to 28 in (PRO100SC soft close, 12 to 28 in).
Full extension or 3/4 extension?
Full extension for kitchen drawers, where you want to reach the back. 3/4 extension is fine for vanities and desks and costs less. Either one mounts to the same box, so you can decide after the box is ordered.
How much weight can side mount slides hold?
Most kitchen grade side mount slides are rated 100 lb per pair, with 75 lb on 3/4 extension versions and 150 lb or higher on file and heavy duty slides. The rating is set by the slide manufacturer, such as Accuride or KV, and covers the pair, not the box.
Do side mount slides work with face frame cabinets?
Yes, with a little help. The slide needs a rear mounting bracket that hangs its back from the cabinet, or spacers that block the cabinet side out flush with the face frame, because the frame usually sits proud of the cabinet side. We stock both rear brackets and spacers in several thicknesses.
Can I use side mount slides on drawers wider than 24 in?
Not on a standard 100 lb slide. Both Accuride’s 3832 and KV’s 8450 cap out at 24 in wide. Wider drawers need a heavier slide or an over travel file drawer slide rated for the extra width, such as KV’s 8505 at up to 30 in.
What is the best type of drawer slide for a dresser?
Full extension ball bearing side mount is the best fit for most dressers, since it is widely sold and simple to replace. A few light antique style pieces run on a single center mount rail instead and are best kept on that type rather than converted. Gritly builds a side mount box to your dresser’s exact opening, 1 in narrower than the opening.
How much room do you need to leave for metal drawer glides?
Side mount slides, sometimes called metal drawer glides, need 1/2 in of clearance on each side, so the finished box is 1 in narrower than the cabinet opening overall. That is the same deduction whether the slide is plain or soft close, and the depth just matches the slide length. Gritly cuts every side mount box, standard or custom, to that rule.
How wide and thick are side mount drawer slides?
Most ball bearing side mount slides run about 1/2 in thick on each side, which is exactly the clearance the box leaves for them. Length is the other size that matters, and it should match the drawer depth. Gritly stocks Würth PRO 3.0 and PRO100 in 10 to 28 in lengths to cover nearly any drawer.
Can side mount drawer slides go on the bottom of a drawer?
No. Side mount slides are ball bearing channels that bolt to the vertical side of the box and the cabinet wall, not the bottom edge. A roller slide fastened along the bottom edge instead is a different type, bottom mount, which takes the same width box as side mount since Gritly builds both to the cabinet opening minus 1 in. Pick the type first, since the two slides are not interchangeable on the same box.
Where can I buy side mount drawer slides?
Gritly sells side mount drawer slides online: Würth PRO 3.0 and PRO100, both full extension and rated 100 lb per pair in 10 to 28 in lengths, plus the soft close PRO100SC in 12 to 28 in, with no 26 in length. Shop the PRO 3.0 slide on its own, already mounted on a standard size box, or added to a custom box with the sides left plain. Face frame cabinets need a rear mounting bracket or spacer, sold separately.
Where can I buy ball bearing drawer slides?
Gritly sells ball bearing drawer slides online, the kind used on the side mount box: Würth PRO100 and PRO 3.0, both rated 100 lb per pair, plus the soft close PRO100SC. All three screw straight to the same plain sided dovetail box, with no notch, drilling or clip needed. Retail orders ship free to all 50 states.
The simplest box we build
Pick a standard size or enter your own, leave the sides plain, and screw your side mount slides straight to it. Dovetailed, cut to the 1/32 in, built in our Las Vegas shop.