Uncleaned as found. Stamped "THE CHAPIN STEPHENS CO." and "NO. 58 1/2". Would have been made circa 1901 to 1915. Fine overall condition noting the absence of alignment pins or any warping which is remarkable in its own right.
Many of the 6-fold rules are manufactured by the likes of Stanley or are left unmarked. While Philip Stanley's Rule Concordance and Value Guide lists the existence of this particular rule being made by Chapin-Stephens, I haven't been able to find other examples online in my research. The difference between the No. 58 & 58 1/2 rule is that the latter is fully brass bound. This rule rules! Top shelf.