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The measurement from the top hook to the bottom of the case is 3 inches. The options I've seen are 3 1/8" and 3 5/8". Looks like I'll be trying 3 5/8". That's more than the 1/4" you mentioned but, I don't see anything in the middle. Thanks!
Details: the leader's flattened wire top hook always hooks on right to left. The lower "D" shaped loop also needs to be adjusted so that the pendulum hangs exactly straight on the leader wire. This is best done before the leader is installed, just hold a little tension at the hook to leader junction and sight down the assembly. The leader/pendulum assembly should be as straight as an arrow, from top to bottom. If not, adjust the lower loop of the leader to make it so.
The pendulum should swing as an assembly, not as two separate parts. If the pendulum hook is teetering on the leader it won't run as well as it should.