There are several types of non-standard self-tapping screws available, each designed for specific applications:

1. Thread-cutting screws: These screws have a sharp, self-tapping point and wide, deep threads that cut into the material as they are driven in. They are commonly used in metal applications where a strong and secure connection is required.

2. Thread-forming screws: Also known as cold-forming screws, these screws don't have a cutting point. Instead, they have specially designed threads that reshape the material as they are driven in. They are often used in softer materials like plastics or wood, where cutting threads may cause damage.

3. Hi-lo screws: These screws have a unique thread design with alternating high and low threads. The high threads cut into the material, while the low threads provide additional stability and gripping power. Hi-lo screws are commonly used in applications where a strong connection is needed in softer materials.

4. Tri-lobular screws: These screws have a specialized thread design with three lobes instead of the traditional flat or rounded threads. The tri-lobular shape allows for easy insertion and removal while providing excellent resistance to loosening. They are often used in applications where vibration or torque resistance is crucial.

5. Twinfast screws: These screws have double-start threads, meaning they have two threads that wind around the screw shaft. This design allows for faster insertion and increased holding power. Twinfast screws are commonly used in wood applications, as they provide a strong grip and reduce the risk of splitting.