a hand-operated press in which a horizontal beam with heavy steel balls attached to the ends gives additional momentum to the descending member used to punch or compress material
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Examples from the Web for fly press
Historical Examples of fly press
The stamp is urged by a fly-press, which cuts them out at one stroke.
Plated buttons are stamped by the fly-press, out of copper-plate, covered on one side with silver at the flatting-mill.