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Bolt Thread Sizes

14K views 34 replies 11 participants last post by  Mikey  
#1 ·
Hi All,

I'm after some advice please. I was wondering if anyone could explain bolt thread sizes to me.

Basically when listing thread sizes for various bolts and screws they are listed as M then a number. For example M10 or M7 ect.

What does this mean? How can you tell what thread size a bolt is by looking at it or measuring with a ruler?

Reason I'm asking is because I'm after a new set of bleed nipples for my MX3 and having trouble saucing some from my local motorfactors. He did say though if I could get the thread size we should be able to match some up. If it's any consilation they have an 8mm head on them :eek:

Any help would be appreciated. :d

Cheers
Mike
 
#3 ·
Perfect Rick, just the answer I was after :d

I have a vernier caliper so I can measure the diameter, just need to figure the pitch out now.
 
#4 ·
Sorry to sound a bit dull:eek:

but would that be the diameter with or without the thread? I appreciate it would be difficult to measure the diamter between the threads.

Just got me thinking back to my metal work days in school, we'd drill the hole the same diamter as the bolt minus the thread and then open the hole out with a tap when cutting in the thread to match the bolt.

Just thinking out loud is all!

Anyone know of a way I could tell the pitch also with out a guage?
 
G
#5 ·
Micky

Take a look here

As for the pitch, you'll get it near enough by measuring the distance between the tip of 2 threads with your vernier (hold it up to the light to make it easier), then look up the standard thread pitches and see which comes closest.

If your not sure, drop me a line, I have data tables for just about every thread ever made :eek:
 
#6 ·
Nice one Pat :d

I shall have a go measuring the pitch as you said. Very usful info there.

I'll hold you to that fella if I get stuck! :eek:
 
G
#10 ·
Whilst it is relatively easy to gauge the diameter of a metric thread by eye, there can be different thread pitches. Whilst an experienced eye can tell the difference between most of them, there are a few unusual ones about

As noel has said, it’s not completely inconceivable that it’s an imperial thread. A ¼” UNF is 6.3mm diameter, with a similar pitch to a M6 thread. Not so easy to spot by eye:)
 
#9 ·
Believe it or not I have actually came across British sized bolts and bleeders on some far east cars. It maybe because some of their components have been sourced in India where they still some use imperial sizes.:)

It may be worth accurately measuring the hex head sizes in imperial just in case. Sometimes it hard to tell as seventeen sixteenths is very close to 11mm for instance.:)
 
#13 ·
Just as an aside,not only does the thread have to be same for the bleed nipples,but the taper on the end of them has to be the same otherwise they won't seal properly.

I have a selection of nipples (oo-er missus!:d) hanging around,I'll dig them out and see what I've got and send you some to compare with yours if you want.

I've sent off my pair off nuts in the post before,you'd might as well have my nipples too!.:eek:
 
#20 ·
Lag sir you are too kind.

But I don't want just your nipples, can I have the hole moobs too :eek::rofl:

I'll be back under the car this weekend so I'm gonna measure them all up and see what we got size wise!

If you don't mind Lag I would love your nipples! :d I'll have to compensate you in some way though.
 
#27 ·
Nice one Lag you star:bowdown::cheers:

They're 7mm I was out measuring this weekend when finishing off the fluid change.

Not sure on the pitch, I think it's 1mm but my calipers only have 1mm incraments, not the best in the world but they usualy do for what ever job I'm doing. I did use my a ruler I have that goes up in 1/2 mm incraments and still seemed to be about 1mm pitch.

Send me your email addy bud, I would like to send you some funds for them if not just to re-imburse your postage.

Cheers
 
#34 ·
I already have!.:rofl:

never mind the screw thread (by the way one of yours is loose) I hope your better with a spanner than you are with song writing.
Spanner?.Mmm.....not sure what one of those is.....anyway,I'm going off topic and I'll get told off agian.:nonono:

Christmas number 1 is mine this year.:d
 
#33 ·