This pillar is 1.00" long, and is intended to be cut to length, used for custom builds that may have thicker stocks.   The outside flange is nominally sized for a 5/8" forstner bit.   The smaller outside diameter is nominally sized for a 7/16" forstner bit.  Both the outside of the flange and of the shaft are sized with the actual diameter just under that to allow for a clean fit, and addition of bedding epoxy (recommended).
 
The inside diameter of the pillar (hole) is = 0.260", which is sized to fit 10/22 takedown screws.  It can also  accommodate up to a #14 bolt (1/4") or a M7 metric bolt freely.  The outside diameter is irregular to increase adhesion.
 
The green anodizing is to harden the aluminum.  It is not visible on the stock from the outside.  However when you disassemble the stock, the green pillar will make it evident that yours has been accurized, and may be suitable for benchrest competitions. 
 
Manufactured by Raven Eye Custom from bar stock aluminum.