Quick question, what size bolt is this?

[Mark A]

Need to order a new bolt for my airgun, but cant seem to find out what the current bolt is. If the OD inc the threads is 4.5mm, is that an M4 or M5 bolt? I thought it was supposed to be either 4 or 5mm, but not bang in the middle.

Thanks

 

[Mark A]

Argh, I cant actually look at that for more than a few seconds .

Just measuring with some cheapo digital callipers. So I think this is possibly an M5 bolt then? Its a BSA Lightning that is about 10 years old, so i'm pretty sure it will me a metric bolt.

 

[Mark A]

My eyes are getting bad, I had to take a photo and blow it up. i count 32 threads per inch. Which I think works out near 0.75mm, so it be the M4.5bolt you mentioned. The only problem is I cant even find any for sale on ebay.

I think i'm just going to have to buy one from somewhere like Chambers for like £5 inc del . Ideally i wanted to use an off the shelf bolt that isn't made out of cheese like the BSA bolt was.

The other option is drilling out the cylinder end plug and then re-tapping it to accept M6 or something. At least then I can easily replace it in future if it strips again. I'll just have to check the plug isn't hardened.

 

[Mark A]

Thanks for the help all. The calliper was £15 or so from ebay so the chances of it being accurate are probably not very good .

Well 2BA seem a lot easier to get hold of than M4.5, so I might give one a try. It would save a lot of messing about if it is right. I can get 30 for £4 for a lifetime supply if they fit

My gun is around 10 years old, but according to the serial number I think the design dates back to the 80s, so there's a good chance they are imperial after all.

EDIT: I think I have confirmed it. While googling 2BA it appears that darts still use this thread to connect the shaft to the head and lo and behold the original bolt is a perfect match in my darts .

 

[Mark A]

Thanks but i think its all sorted now. Ordered 2 x 2BA bolts last night from ebay and they were despatched at 7am this morning 1st class, so should be able to use the gun over the bank holiday.

Have to say this subforum is really helpful. I wouldn't have expected to get an answer at 11pm on a computer forum . I almost just ordered some M5 bolts, so I am glad I asked here first.