'02 Monaco Blue 172
Just bought a compression tester cause my engine definately isn't running correctly and using way too much oil, and also got what I hope is the correct adapter for the 172 (on the far left),
problem is, both adapters seem really tight to screw on, and dont come up to the rubber seal on the main unit, can just about get the one with the nut to screw on with the aid of some mole grips and a spanner on the nut but the one that I think I need doesn't have a nut on so its never gonna go on. This is how far It goes,
is this the adapter I need and should it go on more than this?
I dont want to start taking the plenum off until I know this things going to work and give a correct reading!!

problem is, both adapters seem really tight to screw on, and dont come up to the rubber seal on the main unit, can just about get the one with the nut to screw on with the aid of some mole grips and a spanner on the nut but the one that I think I need doesn't have a nut on so its never gonna go on. This is how far It goes,

is this the adapter I need and should it go on more than this?
I dont want to start taking the plenum off until I know this things going to work and give a correct reading!!