Retro is right. is is the worlds best studfinder. to me far better than the electronic ones. the magnet it in will hold the thing on the wall over a nail for screw.
ten bucks on amazon.
tom
2014 Haulmark 40' Super C on Freightliner Cascadia ISX15 Easton 13 speed
Former Owner 1990 38' Newell Coach 236 8V92
Former Owner 1999 45'8" Newell Coach 526 Series 60
Former Owner 2002 45'8" Newell Coach 608 Series 60
Lol, after Jimmy said "check valve" I thought yes thats what it is!! I saw some scratches on the bottom that made it look like it was possibly dragged on something like a wall and thought maybe it is!! There is so many different kinds but Ive never seen one like it
Love old school
1976 Newell 8.3 cummins allison 6spd
1977 Newell 8.3 cummins allison 6spd