Bayonet screw replacement

[Zang]

Hi all,

Over the last few years, I have overhauled more than 20 manual lenses and I am fairly experienced with working with screws. I don't know what happened (I mean I kind of know but let skip the details here) but I stripped two of the bayonet screws in Contax Zeiss 50mm f1.7.

Extracting those stripped screw was another big story to tell the kids in rainy days but to make it short, I was able to removed them successfully without damaging anything.

Now it's time to look for the screw replacement. I was told in another forum the screws are most likely M1.7 but I am no expert in screw specification. My first question is, does M1.7 specs include both diameter and the step size? In other word, if I order M1.7, will it always fit? Another question is do you know any reliable source to purchase the screws?

Cheers,
Zang

[Stephan]

The "M" stands for "metric".
1.7 specifies the diameter in mm (could that be realistic, that small?), you will need also the length.
Fast search brought up M1.7 in 3/5/10mm length.

[Zang]

The "M" stands for "metric".
1.7 specifies the diameter in mm (could that be realistic, that small?), you will need also the length.
Fast search brought up M1.7 in 3/5/10mm length.

Thanks Stephan. That was my guess, but I was wondering about the thread step. If it's only about the diameter, the thread step can vary, right? That mean there are chances I can get wrong thread for the same diameter. That was my main concern.

The length, the head's dimensions are other factors for sure...

[Hugh_3170]

Zang, the head's shape is important, as it has a bearing on how the length of the screw is determined. 

If the head is a cheese head or a mushroom head, then the length is the length of the threaded portion and shoulder under the screw head.

If the head is a cone head (sometimes also called a counter sunk head), then the length is the overall length of the screw including  the length of the head as well as the length of the threaded portion.

Heads also come in different diameters and depths - just to make things interesting!

Perhaps a photo of one of the "good screws" that you successfully extracted without incident would help us advise you here.

Thanks Stephan. That was my guess, but I was wondering about the thread step. If it's only about the diameter, the thread step can vary, right? That mean there are chances I can get wrong thread for the same diameter. That was my main concern.

The length, the head's dimensions are other factors for sure...

[Bob Foster]

If the screw is in fact a M1.7 by far the most common pitch (advance or the thread over the course of one revolution) is 0.35mm.

If the screw is in fact a M1.7 countersunk head in addition to what Hugh noted verify that the included angle of the conic section is in fact 90°. Most such screws have this angle but I have occasionally seen included angles of 82,100, and 110° . A mismatch of the cone angle may or may not fit but will reduce the rated capacity of the fastener.

For what ir's worth M1.7 screws are not listed in the primary ISO, DIN, JIS, or ANSI standards publications. However, I note that numerous distributors of screws carry this size in what are called JIS compliant fasteners. Sometimes standards organizations do publish updates and/or appendices. If this is the case I don't have access to to verify any added specification. On the other hand. sometimes manufacturers will produce "in between" size screws and claim compliance...  If this is the case examine the head of a good screw from your lens very carefully as the way that manufacturers create such a product in does vary considerably.

Bob

[Zang]

Thanks Hugh and Bob.

I know the head dimensions are important. At the minimum, it should sit low in the screw slot. With all those requirements, I feel the chance I can order the right ones is pretty slim. The pictures of the screw are below.

[Bob Foster]

Hello Zang,

If you fail to quickly find a source in your locale you might check the link at the end of this post after very carefully measuring a good screw.

Bear in mind that the outside diameter of the threaded portion of the screw will almost certainly be slightly smaller than the nominal diameter of the screw; your sample may be a good guide.  Do keep in mind that the screw head diameter can, if necessary, be reduced by careful use of a file. The same may apply to the thickness of the screw head if just a bit must be removed to obtain clearance. The threaded portion can also be reduced in length if required. A set of high quality Swiss pattern needle files in number 4 cut is very useful for such alterations. Do NOT consider any alteration to the underside of the screw head except perhaps adding a bit of chamfer to the periphery if necessary.

A micrometer and a good thread pitch gauge will be helpful, At worst, any machine shop specializing in small parts or watch and clock repair shop will likely be able to help with measurements.

Once you have good measurements I suggest that you search the web for JCIS 10-70 compliant fasteners available from a distributor or supply house close to you first. Failing that, perhaps the following link may be of help.

https://www.metric-threaded.com/Category/Index/16226 The pictures here are generic (not very helpful) but this outfit does offer a good selection.

Disclosure- I've never had any dealings with the company listed in the link.

Bob

[Hugh_3170]

+1

Hello Zang,

If you fail to quickly find a source in your locale you might check the link at the end of this post after very carefully measuring a good screw.

Bear in mind that the outside diameter of the threaded portion of the screw will almost certainly be slightly smaller than the nominal diameter of the screw; your sample may be a good guide.  Do keep in mind that the screw head diameter can, if necessary, be reduced by careful use of a file. The same may apply to the thickness of the screw head if just a bit must be removed to obtain clearance. The threaded portion can also be reduced in length if required. A set of high quality Swiss pattern needle files in number 4 cut is very useful for such alterations. Do NOT consider any alteration to the underside of the screw head except perhaps adding a bit of chamfer to the periphery if necessary.

A micrometer and a good thread pitch gauge will be helpful, At worst, any machine shop specializing in small parts or watch and clock repair shop will likely be able to help with measurements.

Once you have good measurements I suggest that you search the web for JCIS 10-70 compliant fasteners available from a distributor or supply house close to you first. Failing that, perhaps the following link may be of help.

https://www.metric-threaded.com/Category/Index/16226 The pictures here are generic (not very helpful) but this outfit does offer a good selection.

Disclosure- I've never had any dealings with the company listed in the link.

Bob

[Andrew]

How many do you need! A few years ago got them from Nikon Warsaw.
Send me size and address, please!

And

[Matthew Currie]

If shipping is an issue, I am pretty sure I have the right screws, or close enough to work (never throw away the screws when I take an old camera or lens apart) and could tape them to a card and send from Vermont for cost of first class mail to Canada.

There appear to be two different thread pitches here, and I'm not entirely sure which yours is, but the finer of the two is much more common.  I think I could throw in a couple of both, though.

[Zang]

If shipping is an issue, I am pretty sure I have the right screws, or close enough to work (never throw away the screws when I take an old camera or lens apart) and could tape them to a card and send from Vermont for cost of first class mail to Canada.

There appear to be two different thread pitches here, and I'm not entirely sure which yours is, but the finer of the two is much more common.  I think I could throw in a couple of both, though.

OMG, this is the second time you offer me cross-border help! When I feel amazed, I feel bad at the same time about you making effort to help me.

Now, this is not a big issue as the lens has 4 bayonet screws. I stripped two of them but the other two are in perfect condition. I moved those two good ones to the opposite sides, so they hold the bayonet OK. It is nice, at least for cosmetic reason, to fill the empty holes with right screws, though

Regarding the dimensions, the body diameter is 1.66mm, the body length is 3mm (but does not need to be precise as the screw hole is pretty deep), the head thickness is 0.5mm, the thread size is  8 or a little more than 8 threads out of 3mm length. The screw is black as virtually with all other Contax lenses, but color is the last thing I worry about.

Matt, I think I would be totally fine with two screws missing, but if it does not cause you any trouble, I would be very appreciated for the screws! This is by no mean urgent and I hope I'll get a chance to help you with anything

Cheers,
Zang

[Zang]

How many do you need! A few years ago got them from Nikon Warsaw.
Send me size and address, please!

And

Hey Andrew,

Thank you so much for your offer and good to hear from Poland. Not sure if you know but Polish is actually my second language

Matt Currie also offered the screws in his post below so let me talk to him first as he is much closer to me than yourself. If I still have trouble finding the screws, I'll reach out to you for sure.

Dziękuję serdecznie,
Z pozdrowieniami
Zang

[Zang]

Hello Zang,

If you fail to quickly find a source in your locale you might check the link at the end of this post after very carefully measuring a good screw.

Bear in mind that the outside diameter of the threaded portion of the screw will almost certainly be slightly smaller than the nominal diameter of the screw; your sample may be a good guide.  Do keep in mind that the screw head diameter can, if necessary, be reduced by careful use of a file. The same may apply to the thickness of the screw head if just a bit must be removed to obtain clearance. The threaded portion can also be reduced in length if required. A set of high quality Swiss pattern needle files in number 4 cut is very useful for such alterations. Do NOT consider any alteration to the underside of the screw head except perhaps adding a bit of chamfer to the periphery if necessary.

A micrometer and a good thread pitch gauge will be helpful, At worst, any machine shop specializing in small parts or watch and clock repair shop will likely be able to help with measurements.

Once you have good measurements I suggest that you search the web for JCIS 10-70 compliant fasteners available from a distributor or supply house close to you first. Failing that, perhaps the following link may be of help.

https://www.metric-threaded.com/Category/Index/16226 The pictures here are generic (not very helpful) but this outfit does offer a good selection.

Disclosure- I've never had any dealings with the company listed in the link.

Bob

Thank you Bob for the link.

They require an account for purchasing. I have filled the form to create an account but have not got any confirmation back yet. My feeling is they might only deal with wholesale businesses, but let wait for their response.

Cheers,
Zang

[Bob Foster]

A much more restricted selection is available here. https://www.mcmaster.com/screws/system-of-measurement~metric/thread-size~m1-7/.

I did not link to  McMaster-Carr due to their rather dear shipping and handling charges and limited selection.

Bob

[Andrew]

A to checa!

Didn't think that is another Pole in the NikonGear!

And