Mechanic stethoscope probe

[Bonnewagon]

So I was helping a buddy and he had a very nice mechanics stethoscope we used to set the poly locks on his valve rockers. I got home and looked at my own Lisle stethoscope and realized the probe was missing from mine??!!?? And I couldn't remember if the probe was a solid or hollow rod. Looking at ads for the Lisle model it "looks" solid but it's hard to really tell from photos. I scrounged up a length of .140" thick brass brazing rod that I threaded to 6-32 and it fit the disc in the sound chamber correctly and seems good. Anyone know if solid is OK, or is it hollow?

 

[565bbchevy]

Mine is solid, I don't remember what brand though.

 

[Bonnewagon]

I tend to think that's what mine was, but I have that gnawing feeling his was hollow. It was SUPER sensitive. I do know they use a hollow type for finding vacuum leaks, often with a bell shaped end.