What's the knob on OMC shifter below key?

[hdf]

IOn a Grumman 16' aluminum with 70 hp Johnson and on the rear of the OMC shifter there is a knob below the key slot which turns left and right and I have no idea what it controls. Can anyone educate me?

 

[WillyBWright]

Re: What's the knob on OMC shifter below key?

Probably throttle friction to keep the lever where you put it.