The main difference is how the screw pulls and holds the timber.

Part-thread screws

The unthreaded shank can slide freely through the first piece of timber. As the thread bites into the second piece, the screw head pulls both pieces tightly together.

Benefits:

• Better clamping action
• Helps close gaps between two timbers
• Usually the preferred choice for conventional timber-to-timber fixing
• Often faster to drive because less of the screw is threaded

The unthreaded section should ideally pass completely through the first piece. If the thread grips both pieces, it may prevent them pulling together and leave a gap.

Full-thread screws

The thread grips the timber throughout most of the screw’s length.

Benefits:

• Greater withdrawal resistance in the upper section of the joint
• Better control of movement and separation
• Useful for fixing thinner components
• Often better where structural stability matters more than pulling two loose pieces together
• Can provide good reinforcement against timber splitting or deformation when specifically designed as a structural screw

Simple example

When fixing a 25 mm decking board to a timber joist, a part-thread screw is normally best because the smooth shank passes through the board and the threaded section pulls it firmly onto the joist.

A full-thread screw can still work, but the board should be firmly clamped down or clearance-drilled first; otherwise, the threads may hold the board slightly above the joist.

The stainless-steel grade—usually A2 or A4—affects corrosion resistance, but it does not change the basic difference between full and partial threading.