I recently overhauled this Seth Thomas tambour mantel clock with enamel dial. The case is 21 inches long. The movement is No. 89AL, a version of the popular No. 89 movement with solid back plate and active striking on the half hour (as opposed to passing strike).
Both mainsprings are original Seth Thomas springs and are 3/4 inches wide and 0.017 inches thick. They provide plenty of power to operate the movement.
Here is a movie of the clock, showing it operating and striking:
Here is a slide show:
Repair job 4819.
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