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Ask a Mechanic....Captive cap screws a bind


Dear Ask a Mechanic,

I have a set of four aluminum wheels with centre caps secured to the wheel by screw cap sockets (socket cap screws). Through negligence of maintenance most of these sockets (screws) are now seized. Various brand name penetrating oils have not released the sockets (screws), but I haven’t stripped them yet. Is there any hope and/or where would I take the wheels for repair?

Neglectful and Regretting it 

Socket cap screws – also often referred to as Allen or hex head screws – are a very common means for securing the centre caps on aftermarket wheels.

As you’ve discovered, aluminum doesn’t really get along well with steel fasteners, corroding even when stainless steel or anodized fasteners are used. This natural tendency is aggravated considerably by salt, an unfortunate reality for those using wheels like yours year-round.

Since the centre caps are very likely plastic or some form of finished metal, heating the fasteners isn’t an option.

Penetrants can help, but in my experience their effectiveness is hit or miss.

In some instances, an impact driver – the manual type that you strike with a hammer, not an electric or pneumatic gun – will do the trick.

It’s also still very possible that the corrosion-weakened screw will break off in the wheel.

Should the fastener’s head strip, or you don’t want to risk breaking it, your remaining options depend on your mechanical comfort level:

Confident? Using appropriately hard drill bits – starting small, working up – you may be able to drill the screw just to the point that you remove its head. Once the plastic cap is safely out of the way, the remaining stub could be heated/welded-to, Vise-Gripped, or drilled the rest of the way out.

Your local garage or machine shop might be willing to tackle this, or you may have to seek out a wheel refinisher.

These screws are one place where anti-seize seems to be particularly effective, so be sure to use it during reinstallation.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.

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