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03-14-2012, 08:18 AM   #1
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standard screw size on some mounts?

I was wondering if there was any standardization of the screws used on lens mounts. I know a manufacture can use anything they want and they very, but do they often used standard sizes and what is the standard? The only standard I see it could be is iso metric. I have 2 drastically different lenses of different brands that have the same screw size. Thats why I was wondering. I have been modding lenses here and there from canon fd, minolta md ect to k mount but it is always a destructive mod (can not be reversed). The only thing that makes it that way in every case for those 2 mounts is the mount screws have to be shortened to accommodate the thinner k mount. I figured if screws followed a standard and I could get a small selection, some of them might be reversible. It gives me the option of selling the lens at a later date. Also, there seem to be a lot of people that do not like others trashing glass for conversion. It's that only part that I can not get past as far as restoring original mounts. I have another project going where I'm converting teleconverters into mount converters with corrective glass, but I need tiny screws and a tap for the next stage of that, so if I could find tap and screws in such a metric size, it would serve 2 purposes.

Does anyone have any thoughts (if nobody knows for sure, even an I have heard or read ... Would be appreciated).

03-14-2012, 09:02 AM   #2
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I have taken a few lenses and cameras apart, others here have done far more and will likely post as well. In my experience, no, there is not any kind of standard. Even within the same brand, over time the screw size and pitch seem to change. The screws used in Pentax M42 cameras are quite different than those used in later models. Worse many of them are not even standard pitch, or what we consider to be the standard now, though it may have been a standard then. Or maybe it was just what the engineer specified without regard to logistics.
03-14-2012, 09:46 AM   #3
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I kind of wonder if there are any non standard but common sizes that might be found on some lenses too. With the 2 that matched up, they are the size of a 2mm screw (could be 1.8mm) but the thread pitch is different. While I have seen many different screws taking lenses apart, screws similar to this size seem to be somewhat common on mounts with the lenses I have worked on (I had never thought to check and see if they were the same exact thread though). I know that 6-32 and 6-40 are standard english thread screws. 6-48, while not standard so far as I know, is by far the most common non standard screw size on guns and they are easy to find in lots of different lengths, head styles and materials. I'm wondering if there is something parallel with that in lens mounts. I guess only people that do lens repair and have had to acquire screws would know?
03-14-2012, 11:33 AM   #4
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they are not standard across the industry is far as which size they use, but what you have is likely a little used metric size (fine). there is course and fine thread sizes the same as imperial(NC, NF) but are expressed differently for example M8 1.25 is a course thread, and M1.0 is a fine thread.
Metric Thread Chart - by Zero Fasteners

hope this helps

03-14-2012, 12:25 PM   #5
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It seems that there is no official iso fine thread 2mm screw in the chart that slip posted as well as the one I found before that. The only standard size is m2x0.40. There does seem to exist a m2x0.25 screw though. The only reference to it being official is that it was listed in an "extended" iso metric thread chart. There is also mention of it in several tap and drill charts etc.

Looking a little further, it seems to be part of an older British metric standard BS 3692:1967 (ISO 272 equivalent).

I would think that most would use something that was standard at the time (though it might now be an old obsolete standard). They had the choice of getting something standard and available at the time, or they had the choice of getting something custom made (meaning that not only would they need custom screws but they would also need custom taps and dies which would not be the most cost effective approach). Of course the further back you go, the less standard the standards were.

I might look into the m2x0.25 a little more but it seems they are not easy to find.
03-14-2012, 09:23 PM   #6
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As we used to say in the electronics game, the nice thing about standards is that there are so many of them. I've never bothered to identify screws used in various lenses and cameras, because it's easy to see that they are NOT the same. I just save all screws that fall out of photo gear I've disassembled, and fit them as needed by trial and error.

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