BrickLink - Part 99773 : LEGO Technic, Liftarm, Modified Triangle Thin 3 x 5 with Short Supports [Technic, Liftarm] - BrickLink Reference Catalog
Amazon.com: Eske Kouri Gobricks GDS-1002 Modified H-Shape Thick 3 X 5 Perpendicular Compatible with Lego 14720 All Major Brick Brands Toys ,Building Blocks ,Technical Parts ,Assembles (140 Dark Blue(055),120PCS) : Toys & Games