O.D. tube size. Used with brass insert to convert standard brass compression fittings to polyethylene or poly-vinyl tube applications. Sold in bags and also in bulk. No. 30560-04: Size: 1/4in, Material: Plastic, Pkg Qty: 5, Package Type: Bag No. 30550-04: Size: 1/4in, Material: Plastic, Pkg Qty: 50 No. 30560-05: Size: 5/16in, Material: Plastic, Pkg Qty: 5, Package Type: Bag No. 30560-06: Size: 3/8in, Material: Plastic, Pkg Qty: 5, Package Type: Bag No. 30550-06: Size: 3/8in, Material: Plastic, Pkg Qty: 50 No. 30560-08: Size: 1/2in, Material: Plastic, Pkg Qty: 3, Package Type: Bag No. 30550-08: Size: 1/2in, Material: Plastic, Pkg Qty: 50 No. 30560-10: Size: 5/8in, Material: Plastic, Pkg Qty: 3, Package Type: Bag No. 30550-10: Size: 5/8in, Material: Plastic, Pkg Qty: 50