3/8th” or 10mm brake fittings?

[Johnny4428]

Anybody shed any light on this compatibility issue. I purchased a new brake pipe along with brake hoses for my bike a number of months ago I tried to fit this morning but discovered that the old pipe fittings are 3/8th” and the new pipe and hose is 10mm with slightly different thread pitch. Anybody else had this issue?

[Johnny4428]

On further investigation the bleed valve is definitely 10mm so assume originally the brake pipe fittings would have been 10mm as well. So going to modify a tap to chase out original threads.

[K2-K6]

Yes, they are very close and do use the same pipe in many applications.

You get them on cars in changeover years imperial to metric production line switching with the metric and imperial fittings having a different form on the shoulder to indicate which system you are working with.

Honda metric from the start, and so no complications (obviously ignored by previous person fitting that pipe) as you intend, it's more correct if you can encourage the threads back into their original form. It'll probably go in with just a clean out and fresh grease on it to sit in the original thread pitch rather than going with a cut first.

[Orcade-Ian]

Hi Johnny,
I have some new M10x1mm pipe fittings which you can modify with a saw cut to 'persuade' the threads back into position.  Sometimes a bit kinder than a tap which could be a bit fierce.  3/8" UNF is 24 tpi and M10 fine is 1mm - so 25.4 tpi.  Over the length of the pipe fitting that's probably less than 1 thread difference.  Fortunately they are both 60 degree angle threads.
Give me a shout if you are stuck,
Ian

[Bryanj]

The odd thing about Genuine Hona fittings is that the hexagon is 10mm whilst most aftermarket are 11mm

[Johnny4428]

Thanks guys, with a modified M10 x 1.25 tap I managed to find some half descent threads it is now sorted. Can only imagine that the pipe had been made and changed at some point with imperial fittings rather than the correct metric. Don’t think there would been anything imperial in a Honda factory.

[Moorey]

  Aren't the oil pressure switches imperial 1/8 BSPT.

[Johnny4428]

That could very well be Moorey. Wonder if that’s because there’s no metric tapered equivalent?

[Moorey]

  There is a ISO metric taper, very near in fit to NPT. All a bit silly really as it can get a bit dangerous depending on what they are used for
  if mismatched.