You are referring to the pointers or needle valves used in Houdaille shock absorbers. The square pointers were used in 1929 and 1930 and the hex pointers in late 1930 to the end of production. Obtain or borrow a copy of the Restoration Guidelines and Judging Standards book, produced by the MARC and MAFCA Judging Standards Committees and look in Area 23 for more detailed information.