Small Brass or Nickel 90-Degree Trunk Corner Clamps:  CRNR-03
Brass plated steel corner clamps are made for right angles and require 2 nails/screws/rivets to attach to your project (NOT included).  Each leg of this clamp is 1-1/2″ long and 5/8″ wide (38mm by 16mm). From the corner, holes are at 1-1/8″ or 28mm. Hole diameter is 5/32″ or 3.8mm.  CRNR-03, sold in sets of 4 for $10.00, USA shipping included. Brass plated steel or nickel plated steel, your choice.