Holds a standard 5lb fire extinguisher. Mine is printed in PETG with 1.2mm wall thickness and I am quite sure that it can hold substantially more than that. The extinguisher is actually quite stable without the support piece, but it is included just in case you want added clarity. I test printed in PLA and it still has enough snap to lock into place, but it gets hot over here and PLA doesn't survive in the garage. 

No support needed, orient how you want but there should be pretty obvious flat surfaces to auto orient.