Bob,
I think they sell them through Cabelas, but I beleive they are called a "tritium" pin-I use the big one.

Like Rangeball said, they have a pretty big head, but I've owned 2 in the past 12 years or so, the first one lasted around 5 years, and I'm still on the 2nd one.

I use a 20,30,and 40 yard pin. I would have to admit, they would be kind of large for maybe even 30, let alone 40. At 20 yards they work fine, and when it's later, and the tritium is all you can see, it is a very small dot, that is very accurate. My sight is also one that can move up and down, and my 30 yard small sight pin is used as a roving pin, to set at any distance out to 80 yards, for whatever type of shooting I want to use my hunting bow for-say a cat across the field at 76 yards-I just have to try.

So for me, the big 20 yard pin is not an issue, but as Rangeball said, if it's your only pin, you might like something smaller.

Jeff...U.P. of Michigan.