semicircular on the other. Used as a key to hold wheels or gears on a shaft where the end of the key cannot project.

Worm Cam-A cam provided with a "worm" or spiral groove or projection.

Worm Gear-A gear which is grooved in a spiral or "screw" manner instead of being provided with cogs.

Worm and Segment-A form of gearing composed of a worm gear and a sector of a cog-wheel or pinion.

Wrist Pin―The pin which holds the connecting rod to the crosshead.

APPENDIX

HEAT VALUE OF FUELS.

(The following table is given on good authority but will be found to vary considerably from many other tables.)

DIMENSIONS Of Drills for Standard V-THREAD HOLES.

U. S. STANDARD SCREW THREADS

(Angle of threads 60°. Flat at top and bottom for 1/8 of pitch.)