What is copper pipe typesin construction?

Wall thickness. Type K is the thickest, Type L is the middle grade, and Type M is the thinnest, all under ASTM B88 and all sharing the same outside diameter for a given nominal size, so they accept the same fittings. The printed color identifies them: green for K, blue for L, red for M. A thicker wall means more copper, higher pressure capacity in the smaller sizes, and a higher price per foot.

Type L hard drawn tube is the standard call for domestic water distribution above grade in US commercial specs. Type K, often in soft annealed coils, handles underground water service, where many jurisdictions also want a continuous run with no buried joints. Type M shows up where the code and the spec allow lighter duty work. Always read the actual spec section; assuming L everywhere or M anywhere is how bids drift.

Physically, the fittings interchange because all three types share the same outside diameter. Contractually, no: the spec assigns a type to each service, and substituting a thinner wall than specified means a rejected submittal or a tear-out. For the estimator, this means copper lines must carry both size and type in the takeoff, with separate price book entries, because 3/4 inch Type L and 3/4 inch Type M are different materials at different costs.