Push rods attach to a push plate an come in 6 sizes ( 3,4,5,6,7,8 inches long )
There are 2 holes in the top so elastic bands can be used for tension when using elastic tension method.
The tension hold screw is used when using manual tension setting on a push rod instead of elastics.
These rods will not come off or slide threw the push plate since it is securely screwed into the plate. Also made from 6/6 nylon they are very strong but can also flex instead of breaking or bending like plastic or metal rods used on other devices.
Longer rods will provide more tension with elastics.
Shorter rods are good to use when using the tension hold screw making the DTR more compact since less push rod sticks out from the top of the DTR.
The size of your penis has nothing to do with the size rod used. The most common sized used is the six inch push rod.