Tap/Die Advice Please

[155V6]

More help needed putting the back axle back into my MG Express please.

One of the bolts that holds the bottom of the shock won't start going into the threaded part on the axle.I'm going to try tapping it out,but haven't got any taps so need to buy some.The bolt has a 15mm head,so do I need an M15 tap or is it not as simple as that? 

[dollywobbler]

Not as simple as that. Thread size is not the same as head size.

[155V6]

Ok,thanks.What's the easiest way to find the thread size then?

[tooSavvy]

Bolt catalogue (metric bolts... Thread to head)

 

How do we know it is/isn't a 'fine' vs 'coarse' pitch?

 

TS

[castros_bro]

Take the bolt to the tap shop where they will serve you with the right item.

 

https://www.margnor.co.uk/

[Mally]

Machine Mart sell Tap and Die sets quite cheap.

Hold the bolt thread to the tap thread to check pitch.

[michael1703]

Probably 8mm tap possibly 10mm

[155V6]

Thanks for the replies.I've got a fastener shop fairly close,so I'll take a trip there in the week to make sure I get the right size 

[Guest bangerfan101]

There's technique in retapping a hole it's not as simple as just sending the tap straight thru.

[155V6]

There's technique in retapping a hole it's not as simple as just sending the tap straight thru.

I'll be trying to use my light engineering experience from about 25 years ago 

[tooSavvy]

I'll be trying to use my light engineering experience from about 25 years ago 

.... And I'll raise you 44yr

 

TS

[M'coli]

If the thread just needs cleaning up and you've got a spare bolt and can cut an angled slot in one side of it with a hacksaw, that should usually do it. If you only have the one and you're confident of your skills you can get away with the one bolt, cut it shallow, thread it through, then unbolt and rebolt but Loctite in place.

[Guest bangerfan101]

I wasn't trying to be patronising. I've been looking at YouTube vids to try and link you to. But my phone can't stream the videos with subtitles on. And I can't work out how to turn them off.

 

I'm going back to my nvq lvl3 (not very qualified) service and repair of motor vehicles, from college in about 2001 but we were taught to used thread repair taps rather than a cutting tap. Cutting taps we had to use in 3 stages half a turn break the swarf off etc.

 

The tutor was an ex pit engineer and his tails made these 2 hours a week quite comical

[tooSavvy]

Don't Get Me Started....... son

 

TS

[lisbon_road]

It'll be an M10.  Standard is a 17mm head, but metric never seems to be very standard, and automotive are devils for putting smaller heads on.  The thread for an M10 should be 1.5mm.  Fine threads are not so tightly defined in metric, but they take a step or two down so likely to be 1.25mm or 1.0mm but it is likely to be a standard thread on a shock hopefully.

 

Good luck, the spare bolt with a slot in is good for me.

[Kiltox]

It's probably an m10 as said - personally I always measure the bolt using a calliper - 10mm diameter = m10 then use a feeler gauge to check the thread pitch

[lisbon_road]

If you're lucky enough to have thread gauges, fine, but the easiest way to check a metric thread which you think might not be standard is to check it against other standards.  So M10 is 1.5mm pitch and a fine will be either 1.25 or 1.0, and an M8 standard is 1.25 and an M6 standard is 1.0, so if you hold the thread against the light with some standard screws, you can see which it is.  Most metric threads, certainly away from cars are standard. 

 

This message is all a bit over the top but it is harmless!

 

I believe that the American unified threads and BA threads (which are measured in mm) were all better thought out, but better leave that for another day. 

[castros_bro]

Ho no!    It's turned into the dreaded Thread Thread..

 

BSF and Whit are better threads but things like the head size confuse non threadologists.

 

ie  1/2inch whit spanner is not the same as a 1/2inch BSF spanner and neither is  a 1/2inch spanner.

[Honey Badger]

Spend a few quid on a thread gauge and it all becomes very easy to work out, I've got a Gunson pressed steel job, it's been a lot more useful than I thought it would be.

 

https://www.machinemart.co.uk/p/gunson-77106-universal-thread-gauge/

[Guest Hooli]

I wind the bolt into random dies until it goes through easy & then read the thread off the die.

[MikeKnight]

Yeah, another here just saying get a thread gauge, they cheap and so friggin' useful. I have three knocking about the workshop, mostly because I can only find one at a time.

 

I tap and die a lot in my work, it's saved me quite a bit of work. Especially things like manifold studs where they go into weak and sloppy aluminium heads.

 

If the threads are still sloppy after tapping out, you'll need to helicoil it which looks daunting but is actually incredibly easy and ends up with a stronger thread than factory.

[vitessesteve]

If you have a printer you can print out for free some useful tools to identify threads and stuff from the boltdepot.com website. For example: https://www.boltdepot.com/fastener-information/Printable-Tools/US-and-Metric-Thread-Sizes.pdf

 

[DodgeRover]

I've never actually had much luck with helicoils they always seem to come unwound when you remove the bolt at a later date. Timeserts seem better for me.

 

Why are battery nuts always whitworth?

[OwdChina]

To chase thread, or helicoil...............that is the question !

 

 

See here.

http://autoshite.com/topic/5586-mechanics’-know-how/page-3

[Guest Hooli]

I've never actually had much luck with helicoils they always seem to come unwound when you remove the bolt at a later date. Timeserts seem better for me.

 

Why are battery nuts always whitworth?

 

Drop of one of the stronger threadlocks on the insert before fitting sorts that.