This photo shows the input shaft of an air compressor head.

The splined cog-looking disc around the shaft is actually a sort of threaded nut which screws into the larger disc around it. It serves to hold in the bearing on this side.

It may be that this part requires a unique, specialized tool - but I suspect there may be something that is "standard" but perhaps uncommon instead. In many environments a compressor head doesn't require such frequent maintenance that a totally unique tool would be inconvenient.

Note the bolt heads around the splined part don't allow for very much clearance - about 3/16" or ~5mm.

I think given some brute force it probably could be unscrewed using a punch or even a screwdriver used as a punch, but I don't want to damage it.

Possibly an adjustable pin spanner might fit - but the only ones I have are pretty lightweight. Also I think the pins would probably pop out of the grooves (they are usually used in holes instead).

This compressor head is vintage, I think about 70 years old.

enter image description here

  • 1
    $\begingroup$ A think a pin spanner is probably the tool it's designed to work with. Also this is going to sound horrible but you might be able to get a pipe wrench on there enough to loosen it. One other idea: you could make a simple custom punch with a cylindrical end to hammer it loose without damaging it. $\endgroup$
    – Drew
    Nov 25, 2020 at 21:48
  • $\begingroup$ @Drew a beefy pin spanner is what I had imagined too. I don't think a pipe wrench would actually cause too much damage given that the "splines" do not mate with anything else other than the tool itself. $\endgroup$ Nov 25, 2020 at 21:49

1 Answer 1


The plumber's strap wrench is a very practical tool for this job.

Here is one for $ 15.30 from Amazon, just for illustration.

strap wremch

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    $\begingroup$ or the chain version, if the chain is the right pitch - chain wrench $\endgroup$
    – Phil Sweet
    Nov 22, 2020 at 16:53

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