RC Hardware Reference: Screws, Bearings and Springs

"What size is this screw?" and "what bearing goes in there?" are two of the most-asked and worst-answered questions in RC. The answers exist, but they are scattered across manuals, parts diagrams and forum posts, and nobody publishes the underlying system in one place.

This is that system: how RC hardware is named, what the numbers mean, how to measure a part you are holding, and how to find the exact one for your model. It will not tell you the part number for your specific truck — nothing can, and the last section explains honestly why.

Screws: reading the name

Metric — most modern RC

M3 x 12 means a 3 mm nominal thread diameter, 12 mm long.

• The M number is the outside diameter of the thread, not the hole it goes in and not the driver size.
• Common sizes in RC: M2, M2.5, M3, M4, M5. M3 is by far the most common.

⚠️ Length is measured differently depending on the head, and this catches people out:

• Button, cap and pan heads — measured from under the head to the tip. The head sits on top of the surface.
• Flat / countersunk heads — measured from the top of the head to the tip, because the head sinks into the part and is part of the length.

So an M3x12 button head and an M3x12 flat head are not the same overall length, and swapping one for the other changes how far the thread reaches.

Imperial — older and some US-designed kits

4-40 x 1/2" means screw size #4, 40 threads per inch, half an inch long.

Common in RC: #2-56, #4-40, #6-32, #8-32. The number before the dash is a size code that gets bigger as the screw gets bigger; the number after it is the thread pitch.

Metric and imperial are not interchangeable. An M3 and a #4-40 are close enough in diameter to start threading into each other and destroy both. If a screw goes in but gets tight sooner than it should, stop.

Head types, and what each is for

A flat head needs a countersunk hole. Put one in a flat-bottomed hole and it will not seat, it will not clamp properly, and it will work loose or split the plastic as it wedges in.

Drive sizes for hex-drive screws are typically 1.5 mm, 2.0 mm, 2.5 mm and 3.0 mm on metric hardware, and 0.050", 1/16", 5/64", 3/32" on imperial. The drive size is a property of the head, not the thread — you cannot infer one from the other.

Machine screws vs self-tappers — the distinction that saves plastic

This is the single most useful thing on this page.

Machine screws have a uniform, finely pitched thread and go into something already threaded: a metal part, a nut, or a molded brass insert.

Self-tapping screws have a coarser, sharper thread and cut their own thread as they go into an unthreaded plastic hole.

Putting the wrong one in destroys the part:

• A machine screw in a plastic self-tapper hole will not bite properly and will pull straight out under load.
• A self-tapper forced into a threaded metal hole cross-threads and ruins the threads in the expensive part.

Re-installing a self-tapper without stripping the hole

Every time you drive a self-tapper into plastic, it wants to cut a new thread. Do that three or four times and the hole is a smooth tube.

The trick:

1. Put the screw in the hole and turn it counterclockwise (backwards) with light pressure.
2. You will feel and often hear a small click as the screw drops into the existing thread.
3. Now turn it clockwise and tighten.

That click is the screw finding the thread that is already there. It takes two seconds and it is the difference between a chassis you can take apart twenty times and one you can take apart five times.

Also: tighten to snug, then stop. Plastic gives no warning before it strips — there is no "getting tight" feeling, it just goes soft and keeps turning.

Bearings: the naming system is universal

Ball bearings are named by three measurements, always in this order, always in millimeters:

> inner diameter × outer diameter × width

So a 5x11x4 bearing has a 5 mm hole, an 11 mm outside, and is 4 mm thick. That is the whole system, and it is the same everywhere in the world regardless of brand. If you can measure those three numbers, you can buy the bearing.

Sizes you will meet most often

These turn up constantly across 1/10 and 1/8 scale RC:

⚠️ Treat this as a starting point, not a lookup for your model. Measure yours or read your parts diagram before ordering — the same model in a different year or trim can use different bearings.

Shields and seals — the choice that actually matters

Rubber-sealed bearings cost you a little rolling resistance and save you the bearing. For anything that goes outside, that is the right trade every time. Some people remove the outer rubber seal on wheel bearings to cut drag — that is a racing choice, and it means you are now committed to cleaning them often.

Flanged bearings have a lip on one face that locates them against a shoulder. If yours has a flange, the replacement needs one — a plain bearing will push straight through.

Shock springs — where the naming falls apart

Screws and bearings have systems. Springs largely do not.

• Springs are described by rate (how stiff), free length, and wire diameter.
• Rate is not comparable between brands. There is no shared test, exactly like shock oil weight.
• Colors are brand-specific codes, not an industry standard. A "silver" spring means one thing from one manufacturer and something else entirely from another.
• The spring's inside diameter must match your shock body, and shock diameters vary between kits.

So the honest advice on springs is: stay within the brand you started with unless you are prepared to experiment, and record what you had before you changed it.

Measuring a part you are already holding

You need digital calipers. They are inexpensive, and for hardware questions they replace an afternoon of searching.

A screw:

• Diameter — measure across the *outside* of the threads, at the widest point. About 3.0 mm means M3.
• Length — under the head for button/cap/pan; over the whole screw including the head for countersunk.
• Pitch — hardest to measure. If you cannot, take a known screw to compare, or count threads over 10 mm.

A bearing: inner, outer, width — three measurements, done.

A ball / rod end or turnbuckle: thread diameter and the length between ball centers.

⚠️ Measure the old part before it goes in the bin, not after. This is obvious and everybody learns it the hard way once.

Finding the exact part for your model

In order of reliability:

1. The manual's exploded diagram. Nearly every kit-based model has one, and it lists every screw and bearing with a part number and usually the size. This is the authoritative source and it is free.
2. The manufacturer's parts list for your exact model *and year*. Revisions change hardware.
3. Measure it yourself with calipers, then buy generic. For bearings this works perfectly — a 5x11x4 is a 5x11x4 whoever makes it.
4. A bearing kit sold for your specific model. Convenient, usually good value, and it tells you what sizes the model uses even if you only need one.
5. Ask in the forums with the model name, the year, and a photo with something for scale.

The honest gap

There is no cross-brand database that will tell you whether a part from one model fits another. Not on this site, not anywhere. Manufacturers document their own models and nothing else, and the RC world is thousands of models across dozens of brands with no shared parts taxonomy.

That is a real hole in the hobby and we are not going to pretend otherwise by publishing guesses. A wrong "yes, it fits" is worse than no answer — it costs somebody money and a run.

What generalizes is exactly what is on this page: bearings are fully interchangeable by size, and screws are interchangeable by thread, length, head and type. If you can measure those, you do not need anyone's database. Everything model-specific belongs in that model's own parts diagram, and that is where to look.

If you work out the hardware sizes for a model, write them down on its page here — that is the kind of thing that is nowhere else and is worth more to the next person than another opinion.