At the risk of being redundant......and the fact that despite the nature of the original OP question, some seem to be referring to two different labeled manufacturer's springs for some reason, here's some hard data concerning the S&W rebound slide springs, and the "aftermarket" rebound springs manufactured by Wolff.
S&W factory installed rebound slide springs:
Wire diameter, all: .036"
Coil diameter: .185" - ends closed/flat ground
OAL for K, L, N frame: approx. 1.175"
OAL for J frame: approx 1.050"
Wolff "aftermarket" rebound slide springs:
Coil diameter: .190" - ends closed, not ground
rated pounds / wire diameter / approx OAL / # coils
11 .030" 1.20" 17
12 .030" 1.40" 18
13 .032" 1.115" 17
14 .032 1.190" 17
15 .032 1.260" 17
16 .032" 1.360" 17