Paul, take a look at this site.  What do you think? With this no drilling or tapping.
 However we would have to use 1/4 20 push rod.  FWIW
http://www.climaxmetal.com/CRC_Set_Screw_Collars.htm
T.W.

3/8" Teflon is getting so heavy and expensive I am tempted to go back to
a clevis and 1/8th inch thick Teflon. Rev 7.  1/2 inch thick Teflon would
break the bank and the scale.

1/4 inch throttle cable is also over kill.

Paul

I agree on the 1/4 cable,  Just trying to minimize the amount of work to create the button.  If we used the 5/16 variant it has 10-32 thread and an OD of 5/8.  Keep the 3/8 slide, the button will fit with 1/32 clearance either side.  I don' believe it will twist to cause any problems with movement. I too am struggling with the weight and cost for the 3/8 Teflon.  This is a simple solution for a throttle.  Well lets see how well this does on Marks engine then we can reevaluate.

T.W.

It does not take long to drill and tap the off the shelf steel spacers
once you have a rigid set up on a drill press or mill. You can do
two dozen in just a few minutes. The set up take special stops and care.

Paul Lamar