Anglepoise 1227 and 75 screw threads - UK Vintage Radio Repair and Restoration Discussion Forum

Christophe9 · 5th Jul 2022, 2:20 pm

This refers to older Herbert Terry lamps, c.1948-1973. A thread on this forum a couple of years ago concluded that the smaller hinge nuts and bolts are threaded 6BA and the larger tensioning bolt and it's (frequently missing) knurled thumb-wheel are 5BA. I recently had to find a replacement nut for the bolt which connects the fork with the base and found by experience that I had been mistaken in saying it was 1/4" Whitworth. The nut fits a 1/4" Whitworth spanner alright but the thread is 5/16" 26tpi which is not Whitworth or BSF but BSC (cycle thread). M8 Fine thread is so close to 5/16" BSC as to be interchangeable with it. The base nut will rarely be missing but as a Google search for "Anglepoise threads" points to this site I thought it was worth putting the record straight.

Trifocaltrev · 5th Jul 2022, 3:21 pm

Hi, I think you will find the thread is 5/16th BSB (British Standard Brass) and not BSCy. The BSB thread is 55 degrees as is the BSW angle and the BSCy is 60 degrees so therefore they are not interchanable. BSB nuts sizes are the same as whitworth ones.

All BSB threads are 26tpi regardless of their diameter.

Regards
Trevor.

https://en.wikipedia.org/wiki/British_Standard_Brass

Christophe9 · 5th Jul 2022, 4:13 pm

The thread appears to me to be 60 degrees (from measuring of an enlarged photograph of the shank). M8 fine (1mm pitch, 25.4 tpi 60 degrees) fits very well indeed. In practice, for this particulàr purpose, 5/16 BSB, 5/16 BSCy, or M8 fine would all work.

Nickthedentist · 5th Jul 2022, 4:29 pm

And I can indeed confirm that 5BA works for the knurled nut, as you've said.

5th Jul 2022, 2:20 pm	#1
Christophe9 Diode Join Date: Aug 2020 Location: Rugby, Warwickshire, UK. Posts: 5	Anglepoise 1227 and 75 screw threads This refers to older Herbert Terry lamps, c.1948-1973. A thread on this forum a couple of years ago concluded that the smaller hinge nuts and bolts are threaded 6BA and the larger tensioning bolt and it's (frequently missing) knurled thumb-wheel are 5BA. I recently had to find a replacement nut for the bolt which connects the fork with the base and found by experience that I had been mistaken in saying it was 1/4" Whitworth. The nut fits a 1/4" Whitworth spanner alright but the thread is 5/16" 26tpi which is not Whitworth or BSF but BSC (cycle thread). M8 Fine thread is so close to 5/16" BSC as to be interchangeable with it. The base nut will rarely be missing but as a Google search for "Anglepoise threads" points to this site I thought it was worth putting the record straight.

5th Jul 2022, 3:21 pm	#2
Trifocaltrev Hexode Join Date: Nov 2013 Location: Lancing, West Sussex, UK. Posts: 285	Re: Anglepoise 1227 and 75 screw threads Hi, I think you will find the thread is 5/16th BSB (British Standard Brass) and not BSCy. The BSB thread is 55 degrees as is the BSW angle and the BSCy is 60 degrees so therefore they are not interchanable. BSB nuts sizes are the same as whitworth ones. All BSB threads are 26tpi regardless of their diameter. Regards Trevor. https://en.wikipedia.org/wiki/British_Standard_Brass

5th Jul 2022, 4:13 pm	#3
Christophe9 Diode Join Date: Aug 2020 Location: Rugby, Warwickshire, UK. Posts: 5	Re: Anglepoise 1227 and 75 screw threads The thread appears to me to be 60 degrees (from measuring of an enlarged photograph of the shank). M8 fine (1mm pitch, 25.4 tpi 60 degrees) fits very well indeed. In practice, for this particulàr purpose, 5/16 BSB, 5/16 BSCy, or M8 fine would all work.

5th Jul 2022, 4:29 pm	#4
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,844	Re: Anglepoise 1227 and 75 screw threads And I can indeed confirm that 5BA works for the knurled nut, as you've said.