Depending on the stud you buy you will want to also buy the appropriate size carbide drill bit to drill the hole for it. For a one time application I would recommend the type with a button head screw over the ones that need to be counter sunk because that one will need two different size carbides. One to drill the hole and one to counter sink the head of the screw.
A 3/32 size carbide drill is $9.50. A 3/16 is $15.75. This can vary from supplier to supplier but that is what I paid last time I bought from Jantz supply in Oklahoma. I like dealing with Jantz because I'm in Oklahoma and get the stuff I order the next day most every time I order.
I get my studs from Knife and Gun finishing supplies. They are only a dollar a piece. They sell the carbides also so because of shipping you will want to get this stuff in the same place.
What I use is a 3/32 carbide. I mark my hole with a lead pencil. Making sure to place the thumb stud where I want it. Be sure to put the stud on the blade where you expect to mount it, hold the knife fairly level and as you do close and open the blade slowly and controlled leaving the stud where you plan to install it. Watch it as you close the blade. It may move a bit on you but try to do this just briefly so the stud does not move to get an idea of the radius and how close the stud will come to the body of the folder mounted where you want it. This way you want to make sure you don't mount it where it will hit the body of the folder or the corner as the blade opens and closes. Doing that can make a real mess. You'll end up having an extra hole in the blade because you drilled one in the wrong place.
Follow me here because this is very important also. The stud should be mounted on the flat spot of the blade behind the grind line if possible. If you mount the stud within the grind line it will most likely work for a time and then the stud will loosen up. This will repeat even if you use lock tite because the screw isn't flat against the metal and neither is the head of the stud. They both should be flat on the blade.
When you drill do so with a drill press for best results. Set it at a faster speed than a normal twist drill speed. Keep a cup of cool water near by. (this is optional and probably won't be needed but just in case I always have some near the press) Drill a little, clear, feel the blade, if hot, wet the blade. Don't let the blade heat up and for sure don't burn mark it by pushing the drill through too fast.
I have found that it is best to place the blade flat down on a piece of metal on your press table. Something that is scrap but not rough that will scratch up your blade is what I would use. This other piece of metal under your blade is important because it will help to eliminate the very common problem of the carbides shattering upon exit. They are very brittle.
I also advise that you utilize clamps to hold the blade in place when drilling. We are talking about drilling a sharpened blade when it is open and that can be very bad news if it gets away from you. Use a small block of wood to protect the blade from mars the clamp may cause. In other words clamp the blade to the press table but use the sliver of wood to cover the blade and place the clamp on the sliver.
Once the hole is drilled out place the button head screw through it and screw down the stud. Use a small needle nose plier to hold the stud using a small rag to shield the stud from the pliers marking it up. With an allen wrench or torx depending on which you buy tighten it up until it is snug and at the end turn the pliers just a tweak on the other side also. Use locktite if you feel the need but if the stud is flat it should be fine.
The excess sticking out the other end can be taken down with a drum sander or cut off disc. You can also use a belt sander or bench grinder but be careful not to mar it up. If you do mar it use a fine emory cloth to take out the scratches.
Hope that helps. Feel free to contact me if I can be of further assistance.
Don't try this with anything other than a carbide. Cobalt won't work it will just heat up your blade. Oh, and wear eye protection. These carbide can shatter and pop.
EDIT: I want to apologize for being so long winded. But I want to also prepare you for one other possibility before you drill a hole in your blade.
Look at these pics of a knife I did. I do these often for Fallkniven U2 owners. This was the last one.
Here is before I touched it.
Here is after
As you can see if the stud will keep the blade from closing you have some more modifying to do besides just install a stud. If this is the case you will need a variable speed dremmel and a fine 1/2" sanding drum and drum sander bur to make the thumb ramp. Then a fine emory cloth after that to smooth out the lines made by the sander and that is of course if it is an FRN handle we are talking about. If it is a metal body, a very thin walled body or a finely finished wood you may not even want to mess with this. Don't be surprised if you also have to make a minor adjustment on the opposite side for the head of the screw of the thumb stud also. This can be done with the drum sander also.
Fortunately all of these things can be assertained before drilling a hole into your blade needlessly. I hope I covered everything. Good luck. On some knives you can get away with just mounting the stud and not have to worry or mess with modifying the body or handle of the knife.
This one is a good example of that. Hopefully this is more what you will run into as this type is, as the old saying goes, "a piece of cake".
Steve
