Mechanical Enterprises LM
LM is a series of mechanical switches from Mechanical Enterprises, which falls under their “Gold V-bar” family. Few details are known for certain. They are lower in profile, and can be packed in more tightly, than the larger full-travel LFW series gold V-bar switches. Both types were advertised by Tekdata in Electronics Today International, November 1974, page 7, sadly without any clear illustration.
LM switches appear to be targeted towards applications such as calculator keypads, where tight spacing and low profile matter more than switch travel, or where short travel is preferable.
LM and LFW were both covered in US patent 4004121 filed on the 4th of April, 1974.