Mueller brand (made in the USA) soft (annealed) copper in ACR (for refrigeration) and L type (water & gas).
All refrigeration grade copper tubing is designated in OD (Outside Diameter) sizes only and is compatible with flare fittings or brazing method.
All type L copper tubing is specified in Nominal or OD (OD is 1/8" larger than nominal) and can be used with compression, sweat, push-fit (push-to-connect) or flare fittings.
See specs in product listing for wall thickness and other details.
Can be used in conjunction with compression fittings or flare fittings.