Beginners questions

[larry phelan 1Participant @larryphelan1]

Good morning all,

I came across a strange bolt recently, strange to me anyway. It was 110mm long,18mm dia with the first 50mm threaded with a fine thread, not the usual 18mm course.  I assumed it was Metric fine, but I have no such gauges, so I tried my Whitworth set and to my surprise I found that the one for 3/8″ whit, 16 tpi was a perfect fit ! I then began to wonder if it was UNF ?. it seems like a strange mix of systems, or am I missing something ?

Any ideas ?    I bet someone out there knows !

[JasonBModerator @jasonb]

Where did you measure the 18mm? If the shank then a rolled thread would be larger over the crests so possibly 3/4 x 16tpi.

[Andy_GParticipant @andy_g]

It was 110mm long

Further to Jason’s comment: How did you measure the 110mm?

 

It’s normal to classify bolts by the length below the head – if 110mm is the overall length, then it’s likely a 4″ bolt.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, while I do agree with JasonB and Andy_G, there is a 11/16″ Unified 16 Thread (16UN), which is close to 18mm. See page 15 in the link below.

https://www.worldradiohistory.com/UK/Bernards-And-Babani/Babani/Babani-6-Engineers%20&%20Machinists%20Reference%20Tables.pdf

Regards Nick.

[noel shelleyParticipant @noelshelley55608]

13/16 is 20.64mm so a long way off 18mm. 18mm shank and a rolled thread would be about right to give 3/4″ x 16 .  Noel.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Noel, Opps! I should have said 11/16″, which I’ve now managed to correct, thanks for pointing that out.

Regards Nick.

[larry phelan 1Participant @larryphelan1]

Thanks to all for such quick replies. I was not too concerned about the length, just the thread. I never knew there was a 3/4″ by 16TPI as standard. What  surprised me was that the angle of the thread was 55 deg, not 60, the gauge was a perfect fit, and most of the  bolts sold here now are Metric. Whitworth are very difficult to find.

I measured the Dia just under the head and I assume it was a rolled thread, most are, I think.

Just an interesting item, and as they say, “you learn something new every day ”

Thanks again to everyone.

[Howard LewisParticipant @howardlewis46836]

3/4 x 16, or 11/16 x 16 is are standard BSW, BSF or BSP threads.

9/16 BSF is 16 tpi

It won’t be a Brass thread, since they are all 26 tpi

3/4 UNF is 16 tpi, but the thread form is 60 degrees, not 55.

Howard

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