I just repaired a Seth Thomas “Queen Anne” wall clock with time and strike movement. It is a large movement (about 7 1/2 inches tall), much larger and heavier than the standard American movement. In Tran Duy Ly’s book “Seth Thomas Clocks and Movements”, the movement is listed as #85, and the mainsprings are specified as 3/4 wide by 11 1/2 feet long by .018″ thick. On this clock, a previous repairer had messed up the escape wheel teeth. I trued them using the Webster escape wheel tooth straightener, then topped the teeth slightly in the lathe to bring them all to the same length, then carefully removed the burrs. I tested the movement, and the .018″ mainspring seemed to have WAY more force than needed for the time train. I tested a long thin mainspring intended for 31 day clocks: 3/4 x .015″ x 170″, and it had plenty of power for the time train, but was too weak for the striking (it could barely run the strike train until the mainspring was run down 8 turns, but striking was very slow). Thus, I kept the .018″ mainspring for the striking.
After pivot polishing and bushing, I cleaned and assembled the movement. The escape arc is .62 degrees according to the beat scale, and the running arc (not even fully wound up) is 2.5 degrees. Thus, this thin mainspring has plenty of power for the time train. The strike speed sounds normal with the 0.018″ thick mainspring.
Seth Thomas Queen Anne Time and Strike Model:
Time mainspring: 3/4 x 0.015″ x 170″ (length is not critical)
Strike mainspring: 3/4 x .018″ x 130″ (length is not critical)