SteelTek 3/8-in Structural Galvanized Single Socket Tee in the Structural Pipe & Fittings department at Lowes.com
Amazon.com: Structural Pipe Fitting, DIY Outdoor, Use Imagination -1-1/2"Tee-E Short, 3T-8, Aluminum Magnesium, Note: ID of fitting is 1.925, to take nominal 1-1/2" steel pipe which all have an OD of 1.9". :
Adj Flange, 2 in For Pipe Size, Structural Pipe Fitting - 30LX07|30LX07 - Grainger
4 Way Connector | Modular Pipe Connector | Maker Pipe
Cross, 1 1/4 in For Pipe Size, Structural Pipe Fitting - 30LX37|30LX37 - Grainger
926572-7 Structural Pipe Fitting: Base Flange, 3/4 in For Pipe Size, For 1 in Actual Pipe Outer Dia, Base | Imperial Supplies