I need to mount a Canon 24-105mm aperture diaphragm unit to something, but I don't have any screws for it. In the lens itself, it is attached to some sort of mount via 3 screws that screw into the metallic ring around the aperture. Is there a way to determine the size/pitch etc of these threads, so that I can get replacement screws?


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Is there a way to determine the size/pitch etc of these threads, so that I can get replacement screws?

If you've removed one of the screws, then you can of course measure it to determine the size and thread pitch. To get the thread pitch, you can count the number of threads in a given distance, but it's easy to be off by one when you're dealing with small screws. A better method is to use a pitch gauge. If you can have a real hardware store in your area, they may have a pitch gauge and be able to help you.

Another option is to find the service manual for the lens in question. The service manual should specify the size of all the fasteners used, so you'd just need to look up the right part. If you're lucky enough to have a camera store that does repairs in your area, they'll probably have the service manual you need and might be willing to look up the info.

  • \$\begingroup\$ Also do not forget, that, for example, metric and UNC threads may look simillar but they don't fit at all. \$\endgroup\$
    – Crowley
    Nov 21, 2016 at 15:28
  • \$\begingroup\$ Alas, I haven't got any of the screws. I bought a replacement unit, not the lens itself. Any place where these service manuals can usually be found? \$\endgroup\$
    – Bas
    Nov 21, 2016 at 15:43
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    \$\begingroup\$ You'd need to be a service technician to get the service manual, which is why I suggested finding a friendly camera store. Perhaps a more direct route would be to call Canon's customer support phone number at 800-OK-CANON (800-652-2666) and just ask them to help you find the info you need. \$\endgroup\$
    – Caleb
    Nov 21, 2016 at 15:51
  • \$\begingroup\$ I'm gonna have to try the local camera store then. Thanks for the advice! \$\endgroup\$
    – Bas
    Nov 22, 2016 at 13:44

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