Welder's Square 

Welder's squares, sometimes known as fabrication squares allow you to very quickly clamp material into a 90° or 45° position very quickly for welding pieces together. While they are commercially available, they can be quite pricey depending on brand and construction. This is a simple tool that, with some careful layout, can very accurately be built in your workshop. In this example I am building out a 45°/45°/90° welder's square from 2"x2"x1/4" angle iron.
I will eventually be moving all of my welding/fabrication videos to a new channel TX Tradesman, I invite you to join me there.
/ @txtradesman527
Taytools 12" Hardened Steel Protractor - amzn.to/38dxqVz
DeWalt 60Volt Max Cordless Grinder - amzn.to/3sSeJzX
Fein Slugger Dry Cut Saw - amzn.to/3gBqVAx
Markal Silver Streak Marker - amzn.to/3DjLye1
Irwin Vise Clamps - amzn.to/3gDnU2t