Device to prevent injury from rupture of the mainspring of watches
David B. Fitt's Patent 22,174 November 30, 1858

This exotic device was the first mainspring breakage protection mechanism at Waltham. It was applied to the 1859 model KW18 and to the 1861 model KW10. It preceded Stratton's patent (26,715 January 3, 1860) that was developed at Nashua but followed Reed's patent (17,055 April 14, 1857). It was short lived at Waltham since it was replaced with Fogg's patent safety pinion (46,343 February 14, 1865).

Fogg's patent was actually preceded by Burt's patent (44,161 September 13, 1864). Elgin and Waltham elected to share patent rights and pay royalties rather than litigate the two versions of the patent safety pinion. Following their agreement both companies marked their watches simply "Patent Pinion."

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