D&D B/X is, I would wager, the most popular basis for OSR games. Therefore, B/X style ability modifiers are the most common. In case you didn't know, ability modifiers in B/X range from -3 to +3 and are determined like this:| Homebrew Homunculus
Observation 1: Most of the Thief skills in B/X D&D improve in increments of 5%, which makes using a percentile die rather pointless. You can take the percentile (and x-in-6) Thief skills table, convert all the values onto a d20 target number, and it looks like this (TN rounded up):| Homebrew Homunculus