Thread Size Challenge:

[jaydee75]

Here's one that even LAB may have some difficulty with:
I am making new front turn signal stalks for my 75. There are nuts brazed inside the head light shell that the stalks screw into. It is almost a 7/16-20 UNF, but not quite. Can someone tell me what it is?
Thanks,
JD75

 

[frankdamp]

They're probably 7/16" Whitworth Fine, which are 18 tpi (according to Machinery's Handbook).

 

[L.A.B.]

I am making new front turn signal stalks for my 75. There are nuts brazed inside the head light shell that the stalks screw into. It is almost a 7/16-20 UNF, but not quite.

As the stalks are also the headlamp 'bolts' they ought to be 7/16" UNF?

The original stalks must have been screwed into the captive nuts, so in what way is the stalk thread "almost" 7/16-20? Is it the diameter? Thread pitch? Or both?

 

[dynodave]

The originals are a special spot welded 7/16 UNF nut...then chromed.
Since yours is a "brazed" nut repair job it is obviously not original but you should run a tap through it to clean it up...7/16UNF
Prior to late british and commando the light shell nuts I have are 3/8 CEI or maybe 5/16

 

[DogT]

In my S model the bolts that held the halo on were 5/16-26x1 1/8 CEI. That was the Lucas shell. The repro was 5/16 UNF.

Dave
69S

 

[Rohan]

For an 850 Mk1, bought some stainless 7/16 UNF nuts to replace the original chrome half nuts on the outside against the headlamp brackets. Fitted perfecty - bit chunkier than the originals though.

 

[jaydee75]

You guys were right. It is 7/16-20. The nut on mine had a burr in it and wouldn't let my tap in easily. I thought I was stripping the threads.
It is clear now. Thanks again to the board.

JD