right side view in first angle projection

left side view in third angle projection

left side view in first angle projection

right side view in third angle projection

always less than true inclination

always greater than true inclination

only F-V is true inclination

only T-V is true inclination

knuckle

acme

sellers

buttress

improve tearing resistance

improve tightness

improve heat resistance

improve corrosive resistance

Feather key

Peg key

Double head key

Saddle key