What Is an MTB Top Cap?
The top cap (also called a stem cap or headset cap) is the small cap that sits at the very top of your mountain bike's fork steerer tube. It's secured by a single bolt — the top cap bolt — and its primary job is to preload your headset bearings, keeping your steering smooth and play-free.
But for riders who care about the details, the top cap is also one of the easiest and most affordable ways to personalise your build. A quality top cap from HEXCAPS turns a functional component into a statement piece — without touching your wallet too hard.
What Does a Top Cap Actually Do?
- Preloads the headset: The bolt tensions the headset bearings so there's no rattle or play in your steering.
- Seals the steerer tube: Keeps dirt, water, and debris out of the top of your fork.
- Expresses your style: It's the first thing people see when they look at your cockpit — make it count.
How to Choose the Right Size
Most modern mountain bikes use a 1-1/8" (28.6mm) steerer tube, which is the standard for threaded and threadless headsets alike. This means the vast majority of aftermarket top caps — including all HEXCAPS designs — will fit your bike straight out of the packet.
Before you buy, just confirm:
- Your steerer tube diameter (check your fork specs or measure the outside of the steerer — 1-1/8" is almost universal on MTB).
- Your top cap bolt thread size — M6 is standard. Our Black Bolt top cap bolt is compatible with all HEXCAPS designs.
If you're running a tapered steerer (1.5" at the bottom, 1-1/8" at the top), the top cap size is still 1-1/8" — so you're good.
What Features Should You Look For?
Material & Durability
Look for top caps machined from aluminium alloy or high-quality resin. These materials handle trail vibration, UV exposure, and the occasional crash without cracking or fading. Avoid cheap plastic caps that can strip the bolt thread over time.
Design & Character
This is where HEXCAPS shines. Our range covers everything from bold graphic designs to limited-edition drops:
- Drippy Donut MTB Top Cap — a fan favourite for riders who like a bit of fun on the trail.
- RIDE OR DIE V2 Top Cap — for the rider who takes their riding seriously but their accessories personally.
- HEXCAPS FISHEYE Top Caps (Black & Silver) — a sleek, premium look that suits any colourway.
- GRIMHEX MTB Topcap — dark, aggressive, and built for riders who mean business.
- MONEYPIT MTB Topcap — because every MTB rider knows the feeling.
- DEFAULT MTB Topcap — clean, minimal, and endlessly versatile.
We also drop limited edition designs regularly — check out the FREAKBOB, Sassy, and Mike Wazowski caps before they're gone.
Bolt Compatibility
A top cap is only as good as the bolt holding it in place. Make sure your bolt is the right length for your steerer tube stack height. Our Black Bolt top cap bolt is designed to pair perfectly with any HEXCAPS design — no guesswork required. Also, every cap comes with a free bolt!
How to Install a Top Cap
Installing a top cap takes about two minutes and requires only a hex key (Allen key):
- Remove your old top cap bolt and cap.
- Place the new top cap over the steerer tube.
- Thread in the bolt by hand first, then tighten with a 5mm hex key.
- Important: Do not overtighten. Snug is enough — you're preloading bearings, not clamping a wheel. Then lock everything in place by tightening your stem bolts.
- Check for headset play by squeezing the front brake and rocking the bike forward — there should be no clunking.
How to Maintain Your MTB Top Cap
Top caps are low-maintenance, but a little care goes a long way:
- Check the bolt tension periodically — especially after rough rides or crashes. Vibration can loosen it over time.
- Inspect for cracks — if your cap takes a hard hit, check it before your next ride. A cracked cap won't preload your headset correctly.
- Re-torque after washing — if you pressure-wash your bike, re-check the top cap bolt before heading out.
Frequently Asked Questions
Are all MTB top caps the same size?
Almost. The 1-1/8" standard covers the vast majority of modern mountain bikes. If you're unsure, check your fork manufacturer's specs or measure your steerer tube diameter.
Can I use any bolt with my top cap?
You need an M6 bolt of the correct length for your steerer stack. We recommend pairing your HEXCAPS top cap with our bolts for a guaranteed fit.
How tight should a top cap bolt be?
Finger-tight plus about a quarter turn with a hex key is usually enough. The goal is to remove headset play — not to clamp the cap down hard. Over-tightening can damage your fork's star nut or compression plug.
Will a top cap affect my bike's performance?
Only if it's incorrectly installed. A properly fitted top cap keeps your headset running smoothly. Beyond that, it's pure style — and style matters on the trail.
Ready to Upgrade?
Browse the full HEXCAPS range and find a top cap that matches your ride. With designs dropping regularly and limited editions selling out fast, there's never been a better time to ditch the stock cap and ride with character.