Reply To: BRAKE PIPE UNION SIZE

Philip,

If it is not too late ……

I am not familiar with non-metric threads so after I read Richard’s post, I had to look it up. It seems both 7/16” and 1/2″ unf are 20 tpi, but the former has a nominal major diameter of 0.438″.

However, as I said, I checked the male thread on a banjo fitting with a digital Vernier and the major diameter was definitely ½” (actual reading 0.502) with a 0.05″ pitch and those are definitely the dimensions of a ½” unf thread.

The hardware I measured was from a Light 15 so, having seen Richard’s reply, I re-measured the banjo male fitting and then confirmed it was compatible with a selection of other “stock” cylinders, mostly ex-French models.

That confirmed the ½” unf thread to be the common to all of them which is what I expected because Club spares only lists one reference for all models. However, it also confirmed the unit from which I had originally taken the banjo bolt was not an “odd” one that had been retro-fitted at some time.

I have subsequently corresponded with Richard off piste. He tells me has just been working on his brakes and, although the master cylinder was not accessible, he ran a 7/16″ unf tap into one of the other unions where the brake pipe goes to the rear of the car. Although it was a good fit in that union, my measurements still suggest the master cylinder outlet has a different thread, i.e. ½” unf.

If nobody else can offer precise information, I would suggest obtaining a sample of both a ½” and 7/16” male thread and trying both in your master cylinder.

B……