Thread Identification

[Gotty101]

Hello, I could really do with the help of some people with more experience than me. I have a brake balance adjuster, and it has a thread on it that I'm trying to identify so i can buy a matching tap for a project.
Ive measured the OD of the thread and its 18.82mm and ive gone through the thread pitch gauges i have (metric, Unified and Whitworth). Of these the Unified 20UN and 20 whitworth both look to match the threads.

Ive attached a pick of the unit and with the 20uf pitch gauge on the thread. If it helps im based in the UK and it must have been made in the last 5 years. Ive tried a metric 1.25mm pitch gauge against it (thinking it was m19) but it isnt a match.

Could anyone help me identify this so i can get the right tap please?

 

[Gordon]

Possibly 3/4-20 UNEF That would be 19 mm

 

[redhunter350]

To late to investigate further tonight but if it’s clearly an imperial pitch 20 TPI why measure the diameter in metric ? Your measurements equate to 0.7409” which suggests it’s 3/4 x 20 albeit 0.009” undersize, possibly a UN special I.e. none preferred size.

 

[sniffipn]

looking at the photo of thread gauge, it only fits first couple of teeth - so pitch not same as gauge.

is the thread tapered, or parallel?

what does the part connect to - bulkhead/bracket?

could you ask the supplier of the part?

 

[djswain1]

Hello, I could really do with the help of some people with more experience than me. I have a brake balance adjuster, and it has a thread on it that I'm trying to identify so i can buy a matching tap for a project.
Ive measured the OD of the thread and its 18.82mm and ive gone through the thread pitch gauges i have (metric, Unified and Whitworth). Of these the Unified 20UN and 20 whitworth both look to match the threads.

Ive attached a pick of the unit and with the 20uf pitch gauge on the thread. If it helps im based in the UK and it must have been made in the last 5 years. Ive tried a metric 1.25mm pitch gauge against it (thinking it was m19) but it isnt a match.

Could anyone help me identify this so i can get the right tap please?

Looking at your photo it isn't 20UN as per your thread gauge. Is 20UN same as 20 TPI?
It looks like it is a coarser thread.
19mm would be very odd so more like to be 3/4"
What is it fitted to as that may help identify the thread.
Cheers, Dave

 

[redhunter350]

Looking again at your photo djswain is correct the pitch does not appear to match your gauge, try a 19 TPI gauge, this is used on British pipe threads but the diameter you quoted does not match any standard BSP thread.
Where in the U.K. are you located ?

 

[GRAYHIL]

Just a thought
3/4 x 20 tpi unef
or
3/4 x 20 tpi bsc ( A BICYCLE THREAD)
Grayhil

 

[ChazzC]

Looking at your photo it isn't 20UN as per your thread gauge. Is 20UN same as 20 TPI?
It looks like it is a coarser thread.
19mm would be very odd so more like to be 3/4"
What is it fitted to as that may help identify the thread.
Cheers, Dave

UNEF = Unified National Extra Fine:

 

[Gotty101]

Hi guys, I just wanted to say thank you all for your help. I ordered a tap which arrived yesterday 3/4 20 unef. I've just been out and tapped some ally and it fits a treat. As said above the od of the part is a bit undersized, but I will be using the locking nut on it.

Thanks again for your help.

Trev

 

[ChazzC]

Glad we were of some assistance. I was just thinking that the tap must have set you back a lot, but found a 3/4"-20 UNEF tap & die set on eBay for less than US$20 with free shipping (to the U.S.), which isn't bad: I paid US$14 for a 1/4"-40 UNF tap & die set back in March.

 

[Gotty101]

Well by chance there was someone on ebay uk selling a new one for £20. I thought it may not be the best quality but as I'm only tapping ally I thought it was worth a shot.

I've still got a lot to learn, but I do love being in my workshop.

 

[Gordon]

The piece may not have been undersized. If you measure a standard bolt you will probably find it to be slightly less than the base size. Exact OD and exact ID will not fit together.You need some clearance in order to fit together.