I made my hold down pins nearly 3 years ago (at the makerspace before I even bought my own laser) out of Baltic Birch and I’m still using the same set. I keep wondering what everyone else is cutting theirs out of. Now I don’t use my machine as much as some people, but still. Maybe everyone is using draftboard?
I found that the “T” shaped pins tend to lose grip after a while and for some reason. I think they just get slick from the constant rubbing on the metal. Plus they only touch two sides of the hole, but whatever works best for you. I just know that I was frustrated with the pins not holding stubborn material so I came up with a solution that works for me on my Glowforge and scaled up, also works on my Nova 51.
I just used the T shaped pins that are in the Free Laser Designs category and made them out of the $2/board MDF that you can order from Amazon. To be fair, I am always super gentle with everything in proximity of my GF, but I haven’t broken any yet.