Guys -

Here are some actual measurements of siding on single-sheathed freight cars (boxcars):

ATSF Bx-12 #128604 (1)4-3/4" at the bottom of the car side, then (7)3-1/8", (6)3", (3)3-1/4", and (1)5" at the top of the car side. No V-groove. The hat-shaped braces had various dimensions, but were generally 8" wide and were made from 1/4" thick plate and the 2-3/4" hat section stood out 2-3/4". (probably dates to late 1940's)

C&S #13851 Z-braced boxcar (2)2-3/8" boards, with the remainder being 3" and 3-1/8" boards with no V-groove. (probably dates to about 1952)

GN #31000 class boxcar with Z-braces. 5" plain siding.

NKP #8099 war emergency boxcar with Z-braces. 5" plain siding. At Noblesville, Ind.)

I-GN #6342 single-sheathed boxcar with Z-braces. 5" horizontal siding, no V-groove. (dates to late 1940's)

MP #93000 single-sheathed boxcar with Z-braces. (18) 5" horizontal siding boards, no V-groove. (from plan)

M-K-T #79013 (22)5" boards and (1)4-1/2" board. No V-grooves. (dates from late 1940's)

M-K-T #77635 5" horizontal siding with no V-grooves; 3-1/4" vertical boards in doors (with V-grooves). (dates from late 1950's)

M-K-T #95680 5" and 4-7/8" horizontal boards with no V-grooves; 3" vertical boards in doors with V-grooves. (dates from late 1950's)

This is probably more than you wanted to know about single sheathed boxcar siding!

A.T. Kott