I have an industrial camera with a C-mount lens, like this one:

enter image description here

(Source of image, last accessed 2022.11.02.)

You can see a tiny screw on the top of the picture. It is used to lock the focus ring or other rings, depending on the actual lens. How can I buy one, if I have lost the one that came originally with the lens?

I suppose it is some kind of "10 pcs for 1 dollar" thing from eBay or AliExpress? But how can I find it? I tried searching for a long time, but no meaningful results showed up.

(Also a longer one would be more useful than those tiny ones that came with the lens.)

  • \$\begingroup\$ Edmund optics have been helpful for me in the past. They may tell you (or they may just try to sell you a very expensive replacement). Do you have vernier calipers to measure the inner diameter and look it up. That could narrow it down to a couple of sizes (I wouldn't assume metric - US-based optics firms and their suppliers still use a lot of imperial fixings) \$\endgroup\$
    – Chris H
    Nov 3, 2022 at 9:29

2 Answers 2


I managed to check it with a micrometer gauge and a thread comb.

The thread is metric, with nominal diameter 1.6 mm, and pitch 0.35.

After proper googling as @hobbs pointed out, I finally identified the screws. This google search gives the exact results: "M1,6 knurled screw"



You first need to know what the thread size is, which you could find from the manufacturer, or by using a thread gauge. I would be inclined to e-mail the manufacturer, asking for a replacement Iris Locking Screw for your lens. If you go to their website, they have a live engineer chat feature that you could make use of too.

Alternatively, buy a selection box of metric and imperial screws from a hardware store or reputable online retailer, and find one that fits.

  • 4
    \$\begingroup\$ The last C mount lens I swapped out the locking screw on (replacing it with a grub screw to save space), the thread was M2. I doubt you will find M2 screws in a selection box from a hardware store and good luck using any type of thread gauge on a female thread that small. \$\endgroup\$ Nov 2, 2022 at 19:53
  • 1
    \$\begingroup\$ Assuming you do identify the thread, search for a "M# x #mm thumb screw" or "knurled screw", where it's okay (but mildly annoying) if the length is a little too long, but if it's too short then it won't lock anything. \$\endgroup\$
    – hobbs
    Nov 2, 2022 at 20:04
  • 1
    \$\begingroup\$ @PeterGreen Searching on Amazon for "small metric screws" brings up assortment boxes with screws of sizes M1, M2, and many in-betweens. \$\endgroup\$
    – JoL
    Nov 3, 2022 at 4:23
  • 1
    \$\begingroup\$ @JoL On amazon, yes. At a brick & mortar hardware store, very unlikely. \$\endgroup\$
    – Michael C
    Nov 3, 2022 at 8:00
  • \$\begingroup\$ @MichaelC really? Not sure were you're located, but Midwest USA I'd be able to find this in <5 minutes at Lowe's. \$\endgroup\$ Nov 3, 2022 at 15:31

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