I have a Minolta Spotmeter F which I bought second hand a few years ago, without the lens cap. I would like to buy a lens cap for it. The manual does not mention which diameter should I buy. I have to know as I don't think this stuff is so easy to find in a shop.

Measuring the diameter with a rule I find the outer diameter is probably 39mm (should use a calibre to be sure).

I suppose a generic lens cap with diameter 39mm should go, but I consider that usually lens caps are actually indicated with the thread filter mount diameter, which is on the inner side of the barrel. So a cap which is meant to fit a 49mm lens thread is actually a bit larger than that, as it has to cover also the thickness of the metal.

So the question is:
would a generic lens cap sold as 39mm diameter work?

something like this:


although I would go for something cheaper.