Steel Channel 1-1/4" x 1/2" x 1/8" – OmniSteelSupply
Outwater Aluminum H Channel Fits Material 1/4-in Thick Clear Anodized (Satin) Finish Aluminum Divider Moulding 46-in in the Furniture Moulding department at Lowes.com
Superstrut 1-7/8 in. Channel Joiner - Strut Fitting - Silver Galvanized ZA208EG-4 - The Home Depot