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Grub screws in damper collars
Slimy38 - 9/1/21 at 09:45 PM

My adjustable suspension has the aluminium collars for the spring seats, these lock in place with an M6 grub screw. Problem is the grub screw has turned to mush over time. I got it all separated and removed the offending screw, but the replacement ones I bought don't have the correct thread pitch. It's finer on the new screws than it is on the old.

What's the best way of identifying the thread, and what options will there be? Normally I'd measure ten peaks and divide by ten, but these only have maybe three or four so I'm wary that I can't measure it that accurately.

gremlin1234 - 9/1/21 at 10:16 PM

the engineering way is to use a thread gauge,
however, if you take another bolt, and match the threads back-to-back ie hold the threads together with heads at opposing ends, then it should be easy to match.
(but this won't help on mail order parts ;-(
but perhaps you could match it with another longer bolt, then count its tpi.

else give us a photo, and we may recognise it!

harmchar - 10/1/21 at 12:04 AM

A thread chaser repair kit like the attachment is invaluable when fixing up cars n stuff in the workshop. I have the Snap On version of this and it's brilliant.
https://ebay.us/EXDGnE

coyoteboy - 10/1/21 at 07:08 AM

https://www.amazon.co.uk/dp/B071H8GP18/ref=cm_sw_r_cp_apa_i_2EQ-FbHXTN7 3Q

westf27 - 10/1/21 at 09:50 AM

Just drill and tap another hole ?

Slimy38 - 10/1/21 at 10:45 AM

quote:
Originally posted by westf27
Just drill and tap another hole ?


That had occurred to me, I was even wondering whether retapping the existing hole would be sufficient. The collar is aluminium so it wouldn't be a difficult job. I'll see if I can get a guide on the proper thread size and whether I can get the screws at a decent price, then look at a new hole if I have no luck.

Slimy38 - 10/1/21 at 10:48 AM

quote:
Originally posted by gremlin1234
but perhaps you could match it with another longer bolt, then count its tpi.


Doh! Yep, that would be an easier way of getting an accurate measurement! I'll see what I can find as a match.

Slimy38 - 10/1/21 at 12:28 PM

The plot thickens... so the thread matches to an M8 bolt that I had to hand, which according to the book is a 1.25mm pitch. I measured the same as best I could and it is indeed a 1.25mm pitch.

M6 x 1.25 does show up for some fixings (mainly furniture for some reason?) and I can even find taps for that size, but no sign of grub screws. 1mm pitch seems to be the standard one.

So now I'm wondering whether it's an imperial thread. The closest I can find is a 1/4 inch with 18TPI, but that also seems to be an unusual thread.

Has anyone got any suggestions before I dig out my M6 x 1 tap and just cut a new hole?

JMW - 10/1/21 at 12:38 PM

1/4 inch unc, or whitworth for that matter, is 20 tpi (or 1.27mm pitch).

Slimy38 - 10/1/21 at 12:46 PM

quote:
Originally posted by JMW
1/4 inch unc, or whitworth for that matter, is 20 tpi (or 1.27mm pitch).


Sounds good, I managed to find them for a couple of quid so I've ordered some. Thanks for the information.

coyoteboy - 10/1/21 at 02:19 PM

Ignore me, I misread your m6 lol

[Edited on 10/1/21 by coyoteboy]

gremlin1234 - 10/1/21 at 03:37 PM

quote:
Originally posted by Slimy38
quote:
Originally posted by JMW
1/4 inch unc, or whitworth for that matter, is 20 tpi (or 1.27mm pitch).


Sounds good, I managed to find them for a couple of quid so I've ordered some. Thanks for the information.

1/4 whit. is the standard 'tripod' thread for small cameras. so they may give you something to gauge it against.

Slimy38 - 10/1/21 at 05:05 PM

quote:
Originally posted by gremlin1234
1/4 whit. is the standard 'tripod' thread for small cameras. so they may give you something to gauge it against.


I just so happen to have a small desktop tripod, and yes, it screwed in perfectly! Thanks for the suggestion, that confirms I have the right ones on the way.