I get mine from Buddies. From them they mark the bottom of the slug with a line and match it to a line scribed at the center of the bottom of the hole. The pitches are not part of the thumb mold. They drill the pitches into the hole the mold goes in. Never had a problem.

I use them.  They are great, every ball feels exactly the same.  I highly
recommend them.

Nick, is it hard to line up the molds in the thumb hole to get the pitches and lateral part of the thumb positioned right?
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"Whenever I feel the urge to exercise I lie down until the feeling passes away."

Brick

 I have been using molded thumbs for the last 3 years, best money I ever spent on bowling.

I use custom thumb molds and I like the consistent feel of the thumbhole
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Ken - aka "dpunky" - Certified USBC Level I Coach

Used them for at least the last 6 years and love them.

Like BrunsNick said they make a small notch on the center line so that the mold picks that up, it is on the back side of the thumb so you don't feel it. When the insert is made from the mold that leaves that small mark on the insert and that mark is lined up on the center line of the new ball.

As long as the new thumb hole is drilled at the same pitch then the inserted thumb insert will be oriented and pitched the same way.

The mold will pick up every little nuance of the thumb hole, bevel, taper, etc.

If you leave tape in the hole it will pick that up as well including the texture of the tape.

Just be sure to use a thumb hole in a condition (size) that you can use when your thumb is at it's maximum size. You can still add tape when your thumb shrinks.

Can these molds (slugs) be done at home so they are ready to be handed to your driller when you have a new ball to be drilled? Who makes these molds?

Thanks BG