L063 is made from cold rolled steel with hand inlayed copper bars. SSL063 Shanks are made from stainless steel and the mouthpiece cold rolled steel with hand inlayed copper bars.  Shank length for the Loomis is 8" and 7" for the NSBA, Mouthpiece width is 5", Port opening width is 2",  Port height is 1 1/2" and the diameter of the mouthpiece is 3/8".  All measurments are approximate, slight variations can occur with handmade bits.
The Medium Port comes in 3/8” and 1/2” diameter.  The smaller the diameter the increased possibility for severity.  The point of pressure is more concentrated on the smaller diameter.  more tongue pressure so less tongue relief. The Medium Port has a suitable amount of tongue relief, with a minimal amount of palate pressure. The Medium Port is going to apply pressure to the lateral bar space. The Medium Port is a very popular bit in our line, because many horses get along with the lateral bar pressure.