staked rivet

[SlyOne]

On some folders the bolsters are held in place by a small internal rivet not seen from the exterior. This rivet goes into a blind hole on the part of the bolster that will contact the liner. In any event I have been trying various method and I think I have it. Drill a shallow 1/16" deep blind hole. Drive the rivet/pin into this hole. Now use a "setter" to dimple around the pin to push metal against the pin and hold it tight. I used a needle file- pointy tip to dimple and VERY lightly tapped the butt end of the needle file. This set the pin so tight I can't pull it out. The protruding pin goes through a hole in the liner and is peen hammered to hold bolster to liner.
I realize some of you folks are probably thinking...So what, everyone knows that, but I didn't know how to hold a bolster to a liner before trying this method.

 

[Busto]

Would this be on a "Slipjoint" folding knife...like grandpa's old knife?

The preferred method is to drill through both bolsters aligned with the pivot hole of the blade and peen the pin on both exterior sides of the bolster that will securely
hold the bolster and the small amount of excess pin can be ground down to blend with the outside of the bolster and much more secure method.

 

[Stacy E. Apelt - Bladesmith]

I would be willing to bet that those bolsters you though had "hidden" pins were actually drilled all the way through. Done properly and with a pin matching the bolster material the pin will become invisible.