to reduce friction

to facilitate slipping of balls

to prevent the lubricant from flowing out

to maintain the balls at a fixed distance apart

square threads

acme threads

knuckle threads

buttress threads

in a direction perpendicular to the cam axis

in a direction parallel to the cam axis

in any direction irrespective of cam axis

along the cam axis

Correct

Incorrect

d = t

d = 1.6 t

d = 2 t

d = 6 t