This is a group of 6 (six) different soft cover booklets published by the Industrial Press in 1908-1909 of their Machinery's Reference Series. The included copies are #12- Mathmatics Of Machine Design, #13- Blanking Dies, #15- Spur Gearing, #16- Machine Tool Drives,  #17 - Strength Of Cylinders ,#20 - Spiral Gearing

Each issue is about 40 pages long, and the size is about 6" x 9". Some have loose end covers, but are complete and quite clean. Some great early technical information and illustrations.

Good luck & thanks for looking !

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