How do the pins we see on full tang knives hold the scales to the tang? Are they like rivets with the actual diameters less than what is visible? How do you apply them?
I want to replace the handle scales on a WWII machette and need some advice.
Your help will be appreciated.

Being far from an expert, I think the pin diameters are consistent. The scales are epoxied on as far as I know. At least that's what I did when I made a couple of knives for my own use. Thank you.

Sometimes the hole is slightly tapered and the pin carefully peened .There are special screws that can be used .Take a look at the various types in www.knifekits.com The scales are epoxied in addition.

Epoxy.

Can be done with pins or rivets.

The straightness of diameter of the pin or rivet will depend on the hole that has been bored through the tang for the holding device. If it is obviously skinny (1/8" to 3/16" in diameter) you may want to use a cutler's rivet whose ends are larger in diameter than the waist.

Scales should be epoxied on as well as pinned or riveted. See Knife and Gun for their epoxy ... REALLY good stuff!

http://www.knifeandgun.com/

Sand the tang to expose fresh metal. Do NOT polish it! Leave it rough. Clean the tang and scales with Acetone before applying the epoxy. Check the scales for their solubility in acetone before using any on them. (Try a little on a 1-Tip on the back side.) Clean up as much of the excess as possible before it hardens. Will take 3 days to harden completely. You can accelerate the process after 12 hours by warming to the lowest baking heat your oven will deliver ... usually abt 170F. Warm for about an hour and let cool. Epoxy will be fully hardened.

& make sure those pins aren't too tight a fit or they will split the scales! Thus the reason for epoxy on the pins too.

The pins are just bricks to hold the place, the strength comes from the epoxy.