A lot if not all early telephone openwire strung on crossarms requiring six or more wires (by New England Telephone and independent companies) commencing in the 1880s utilized six-pin crossarms as seen here. Side pin brackets were pretty much the rule if the line called for four or less lines. Owing to the popularity of telephone service in subsequent years, 10-pin crossarm construction began to be pretty much standard for new builds and pole upgrades around 1910.

Insulators (including early New England Tel. & Tel. Co.) were reused by Ma Bell if in good condition as well as other pole-line hardware.

This made for some really nice rusty, crusty iron and steel hardware (especially crossarm braces with "pock marks" from MANY decades of age upon them) along with old NET&T insulators of all sorts including porcelain spools and brackets if you are into this stuff surviving into today's collectors' hands ;-)