Note that the crossarms in this image were affixed to their pole via two diagonally spaced lag screws. This was the earliest method of mounting crossarms to communications and earliest (1880s) electric utility poles. By around the mid 1890's a single standard through-bolt was introduced for this method. The double-lag crossarms sometimes had braces as well, the latter coming upon the line-hardware scene also in the 1890's. Single-hole-mounted crossarms became standard for pretty much everyone soon after 1910. Of interesting note, some crossarms were pre-drilled with holes for the diagional lags *and* through the center, so that the user could mount their arm using either method.

Speaking of hardware, crossarm braces typically were 28 or 30 inches long. Electric utilities have long standardized the 28-inch ones. I am not sure which size(s) the Bell System and Western Union companies used as standard with these in their early years. However it seems like 30-inch braces were utilized by both companies when mounted *over* the crossarms as seen here and slightly shorter 28-inch ones when installed on the inside of the crossarm (as seen a lot in later years).