pressure fittings

[Bootlegger]

  Some time back I remember seeing a question about pressure fittings, the question was which is better for stunt, 4-40 or 6-32.
 I don't remember the suggestions as to which is better, so I'm asking again.
   Thanks, Gil

[john e. holliday]

You talking about pressure fittings or mounting bolts.  In reality a lot depends on the engine being used.   

[Bootlegger]

 Pressure fittings to create muffler pressure to have a steady pressure to the uniflow on the tank.
  Didn't mean to create confusion. Thanks for pointing that out Doc...

[john e. holliday]

Well I have several Fox mufflers that have 4-40 threads.  On the OS mufflers I think they are 6-32.  Which do you need or are you just adding one to a muffler?

PS: Opening in the Fox is 1/32" jeh

[Paul Smith]

Also M3 or M3.5.

In the past, 4/40 was pretty much standard, so you could insert the pressure fitting in lieu of one of the backplate bolts.  

A crankcase pressure fitting needs a tiny hole to restrict the pressure.

A muffler pressure fitting needs a gapping hole to get all the pressure it can,  Thus, a muffler pressure fitting would be better off with a 6/32 or M3.5 thread.  Or for that matter, a chunk of 1/8" tubing glued in with high temp epoxy.

[Bootlegger]

Doc, I sent ya' a p m..  Thanks, Gil