The letters K,L,M denote wall thickness of copper pipes. Which is the thickest and which is the thinness. Please give other designations if there are more.

Hello Carnetta50,

Types K, L, M, DWV and Medical Gas tube are designated by ASTM standard sizes, with the actual outside diameter always 1/8-inch larger than the standard size designation. Each type represents a series of sizes with different wall thicknesses. Type K tube has thicker walls than Type L tube, and Type L walls are thicker than Type M, for any given diameter. All inside diameters depend on tube size and wall thickness.

Copper tube for air-conditioning and refrigeration field service (ACR) is designated by actual outside diameter.

Type "K" is stamped in Green, type "L" in Blue, type "M" in Red and DMV in Yellow.

Type "L" copper is used in residential construction for both hot and cold water systems.

Hope that will answers your question...

Milo

Here you go:
http://www.sizes.com/materls/pipeCopper.htm

I'm curious! Why are you asking?
Is this a test question? Cheers, Tom