That actually looks like a top end cap for an old Costco shelving unit.
Amazon.com: Chia Whalen Post Insert for Costco, Plastic Shelving Connectors, and SAMS Club, 5-Shelf Heavy Duty Steel Shelving Unit, Corner Connectors for Building and Alignment : Tools & Home Improvement
I am 6'4'' right around 240 lbs. and wasn't very comfortable until I put the Misch Big Boy Brackets on. Huge difference in comfort and adjustability, I now have plenty of leg room.