double-threaded

Consisting of two threads twisted together; using two threads.

double-threaded worm

Having two screw threads instead of one; said of a screw in which the pitch is equal to twice the distance between the centers of adjacent threads.

A multiple-threaded product is one having two or more threads cut beside each other (imagine two or more strings wound side by side around a pencil). Standardized products such as screws, bolts, and nuts all have single threads; a double-threaded screw has a lead equal to twice the pitch, a triple-threaded screw has a lead equal to 3 times the pitch, and so on.