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Tap and die set


daverclasper
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There are lots of "imperial threads".  The original British threads were Whitworth.  Pipe and fine.  Known as BSW  BSP and BSF.  These all have different thread angles and the pitch is given by a number which is the number of threads per inch.  All threads are based on the size of rod they are cut into. so 5/16ths is a thread cut onto a 5/16ths rod.  The hole in the nut is less than the the diameter of the rod as bits of it have to stick into where the metal is cut away on the rod.  The imperial system is further complicated by automotive thread systems UNC and UNF probably (as I have been told) American systems.  These are the ones you will come across mostly on our traditional motors.  Things like sump and drain plugs are BSP T for taper.   The heater union on the water pump will also be BSP to make the "plumbing" standard.  The pinch bolt on a dynamo might just be UNC but I suspect its BSW.

Now this modern metric stuff is again based on the rod the thread is cut into.  M8 is cut into an 8mm rod. but the pitch is given in mm. Watch out for the pitch differences! M8 x 1 will not work well with M8 x 1.25.

To check compatibility of pitch lay your bolt alongside the test bolt.  If the pitch is the same they will engage.  Any  small difference will cause the bolt to ride up and not engage.

Then there's B.A. "British Association" threads used mostly for electrical work.  These, despite being British are metric!  I know, why bother having british metric?  I was so pleased when I found out these threads are used for bicyle mudguards and that the foreigners had to use british threads on their bikes.  Of course as its metric based their offworld bolts will fit.

In short you'll need to make sure that you use UNC or UNF taps and dies for the majority of you car work.  Or Rawlplugs!!

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  • 5 weeks later...

Depends what cars you are working on - my AC and Jaguar are both predominantly BSF and BSW, with all small fasteners on both cars being BA.  Engine parts tend to be a mix of UNF and UNC (unified fine and coarse).  The AC has an American engine, so I'd expect UNC threads on that, but I was a bit surprised they were so prevalent on the XK engine.  Cars from the fifties and earlier used BA liberally for small mechanical items, body fittings, everything on the dash etc.  My Series 2A Landie is also almost exclusively Whitworth and BA.

As a result I have several sets of taps and dies, mostly from http://www.tapdie.com/ .  Their range is huge and quality very good - as usual with tools, you get what you pay for.  I only use split dies, so if I'm cleaning up a thread I can screw the spreader screw in and the die takes a light cut only.  If cutting a new thread I usually do it in two or three passes until the thread fit is snug and not loose.

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On 27/09/2020 at 15:01, Prince Brainier of Meccano said:

There are lots of "imperial threads". 

Now this modern metric stuff ...

Watch out for the pitch differences! M8 x 1 will not work well with M8 x 1.25.

At this point a former colleague would say "You know the great thing about standards? There are so many to choose from!"

I've just identified a threaded hole which is missing its set screw (on my 1960's Moulton bicycle) as 2BA. Now, do I source a 2BA screw or re-tap to M5???

Cheers, Richard

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On 26/10/2020 at 23:04, Roger K said:

Depends what cars you are working on - my AC and Jaguar are both predominantly BSF and BSW, with all small fasteners on both cars being BA.  Engine parts tend to be a mix of UNF and UNC (unified fine and coarse).  The AC has an American engine, so I'd expect UNC threads on that, but I was a bit surprised they were so prevalent on the XK engine.  Cars from the fifties and earlier used BA liberally for small mechanical items, body fittings, everything on the dash etc.  My Series 2A Landie is also almost exclusively Whitworth and BA.

As a result I have several sets of taps and dies, mostly from http://www.tapdie.com/ .  Their range is huge and quality very good - as usual with tools, you get what you pay for.  I only use split dies, so if I'm cleaning up a thread I can screw the spreader screw in and the die takes a light cut only.  If cutting a new thread I usually do it in two or three passes until the thread fit is snug and not loose.

Just ordered some taps and colbolt drills for work 👍

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On 27/10/2020 at 19:22, rlubikey said:

At this point a former colleague would say "You know the great thing about standards? There are so many to choose from!"

I've just identified a threaded hole which is missing its set screw (on my 1960's Moulton bicycle) as 2BA. Now, do I source a 2BA screw or re-tap to M5???

Cheers, Richard

2BA is easy enough to find.  Namrick stock them, amongst others.  Slotted head, usually - round or countersunk.

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  • 3 weeks later...

I (still) have some 10BA nuts/bolts and (8-6-2) and washers. From my "yoof" in the days of making model boats and planes!. Mostly Brass, but some steel too. Residing in a "Old Holborn" tobacco tin!. Every Blue moon one comes in handy for repairing some old bit of "tat". Or glasses.

And a good source of the "odd" tap/die or die nut is often scrummaging about at Auto Jumbles.

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PeteH have you been looking in my garage, 

When my dads old secretary died a few years ago when cleaning the garage out it was a minefield of old bits incl taps ad dies of all sizes and threads plus other tool goodies, including the old big Macintosh's tin of railway detonaters like starter gun caps was around 2kg of them. I took them to the police station & I was there over an hour filling in forms and answering questions!

Sec's husband also worked for dads Co. he was was Mr.Fixit could do anything. Mind you looking at the electrics and fittings in his garage I'm glad I didn't let him loose at our house, the things he made cigar box's into!

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