What is the difference between a Canon and Nikon lens cap?

Question

I found a nice project on Kickstarter that I would like to fund: Camera Lens Cap Holder

But it's listed that there will be 10 different lens caps sizes for the holder:

From the site (as of June 7, 2011):

52mm, 55mm, 72mm & 77mm for Nikon, Pentax, Fujifilm, Sony, Pro-series and vintage lenses

46mm, 58mm & 67mm for M4/3, Cannon and Nikon lenses

40.5mm, 49mm & 62mm for M4/3, Olympus and vintage lenses

What is the difference between a Canon and Nikon lens cap, in terms of it's fitting?

Specifically, I have a 72mm lens for my Canon, so does the 72mm lens cap holder listed for the Nikon here not fit my Canon lens cap?

Answer

Lens caps that are attached to filter thread can easily be shared between different brands. The sizes listed here are frequently used by given manufacturers. So yes, a 72mm Canon lens cap will fit a lens cap holder with 72mm filter thread, even if it appears to be "for Nikon".

Comparing lens caps of Canon and Nikon, Canon's lens caps are usually based on simple plain design with two release buttons on mutual sides. Nikon has those for point-and-shoots; the ones for (d)SLR lens use snap-on design (i.e. you can pinch the center to release), which is much more convenient to operate when your lens hood is on. Some Pentax lens caps are also using similar design.

Some lenses use a different mechanism for attaching a lens cap, slipped on lens hood - usual suspects for this solution are ultra-wide, fish-eye, and vintage lenses. Their lens caps are generally specially made for the lens model and cannot be used on different lenses. These lens caps do not use millimeter designation.

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