The pin is actually "bradded" on both sides, so you might have to drill with a slightly oversized bit, a little, and then use a punch.Make SURE you find the exact center of the pin before you drill. You will probably not be able to reuse your old pin. I always use a 1/8" new pin. There should be a small bit of countersink on each side of the hole, if not, use a bit slightly larger than the hole, and countersink very slightly.(This will be where the new pin will be bradded). To install the new pin, chuck your 1/8" bit in your drill press. Then clamp your bolt carrier in your drill press vice, where the drill bit will pass through the hole in your bolt carrier when you lower it. Then screw your new gas piston into the bolt carrier, making sure nothing moves. Then drill through bolt carrier hole and new piston at the same time. Trim new pin about 3/32 longer than the length across the bolt carrier, and install. Use a small ball-peen hammer to brad both sides of the pin into the countersinks. Then, file and sand to perfection.