I have additional info from a 1970 Shooter's Bible on the Pachmayr's:
1M: Colt Police Positive, Detective Special (Old Model)
3S, 3M, 3L: Colt Official Police, Officers Model, Python, Trooper in Small, Medium & Large thickness
4S and 4L: Colt Shooting Master, New Service in Small and Large thickness
7S and 7L: Colt Cobra, Detective Spl, Police Positive (New Models) in Small and Large thickness
2M and 2L: S&W J Frame Sq. Butt in Medium and Large thickness
6S, 6M and 6L: S&W K Frame Sq. Butt in Small, Medium and Large thickness
8M: S&W J Frame RB, Medium thickness
9L: S&W N Frame, Large thickness
The number generally corresponds to the shape, length and curvature of the front grip strap and relationship to the trigger guard which of course is different among the Colts as wells as among the S&W models. The S/M/L designation is for how "thick" the adapter is from the rear going forward from where it touches the grip strap, and how much material is under the trigger guard where it would rest upon your middle finger.