what bolt size is this?

[GazK]

I'm trying to size a bolt from a 1980s bike so I can get a replacement. It is the bolt which holds a downtube gear shift lever in place (screws into a band on shimano altus fitting). Its diameter over the threads is 4.3mm. This doesn't seem to map to either a whitworth or a BA thread, but I know it aint metric cos M4 is too small and M5 is too big.

Can anyone help?

 

[Grasen]

I'm trying to size a bolt from a 1980s bike so I can get a replacement. It is the bolt which holds a downtube gear shift lever in place (screws into a band on shimano altus fitting). Its diameter over the threads is 4.3mm. This doesn't seem to map to either a whitworth or a BA thread, but I know it aint metric cos M4 is too small and M5 is too big.

Can anyone help?

back in the old days there was japanese and italian standards
if I remember correctly japanese was M 4.5 and italian M5
today its all M5

if anybody has an old 1970'ish shimano service instruction sheet for downtube gear levers then we could check. usually both sizes were marked.

 

[Grasen]

 

[GazK]

back in the old days there was japanese and italian standards
if I remember correctly japanese was M 4.5 and italian M5
today its all M5

if anybody has an old 1970'ish shimano service instruction sheet for downtube gear levers then we could check. usually both sizes were marked.

Thanks Grasen, that makes sense - I just checked and an M5 bolt is 4.8mm over the threads - i.e. exactly 0.5mm larger.

So, if it is M4.5 - where the hell would I get M4.5 button head bolts? If google is correct then the answer is "nowhere".

Alternatively I could tap the band-on out to M5, but I'm not sure if there's enough metal there.

 

[Gerry Attrick]

Assuming it is not the screw illustrated, could you drill the band to clear a suitable nut and bolt?

 

[Grasen]

try and drill
or
ebay for a M5

 

[GazK]

try and drill
or
ebay for a M5

It might help if I explain what I'm trying to achieve.

Here is the band-on in question:

I'm fitting downtube stops, like this:

At the moment I'm using the M4.5 hex head bolt that came with the band-on, but a) its fugly and b) I'm having to pack it out with a couple of washers cos its too long.

The downtube stops came with a nice pair of M5 button head allen bolts. I'd like to use these but I'm worried about the thickness of the band-on if I tap it out.

Gerry, I can't quite grasp your nut/bolt idea - where would the nut go?

 

[Gerry Attrick]

Ah. Now I see your photographs I understand what you are trying to do. Forget my suggestion.

Just a thought though, have you tried a supplier of old bike bits, such as

http://vintagecycles...kes/index1.html

http://www.oldbiketr...co.uk/index.php

http://www.framebuilding.com/index.htm

or indeed our very own Hilldodger?

If you have an old fashioned bike shop nearby, it could be worth a try.

If all else fails, you may need to replace the band on with a modern version.

Oh, one last thought. SJS Cycles seem to have an enormous stock of older bike bits.

 

[brodie]

I would cut down the bolt to make it shorter, so that you can use one washer. I don't think it looks so bad, of it's a matter of taste whether it or an allen bolt looks better.

I wouldn't tap it out, it doesn't look like there's much metal there.

 

[PaulSB]

I can't add anything useful here but wanted to comment this thread exemplifies the astonishing knowledge levels which exist on the forum and help make it such an interesting place to be.

 

[Fiona N]

Let me look in my box of nuts and bolts - coming from a family of engineers, I'm a compulsive collector of any potentially useful bits and bobs so have a collection of metal tins with nuts, bolts, little springs, gromets and washers from 30 years of bikes