Screwdrive

Screwdrive, in fastener terminology, refers to the pattern on the head of a screw that accepts a driver bit or tool. The drive is the interface that transfers torque from the tool to the screw and also helps align the screw during driving. Different drive types are standardized to be interchangeable across tools and fasteners within a given family, though compatibility requires matching the exact drive shape and size.

Common screw drives include slotted, Phillips, Pozidriv, Torx, hex (Allen), and square (Robertson). Slotted drives feature a single straight groove and are simple but prone to cam-out and misalignment. Phillips drives use a cross-shaped pattern designed to allow controlled cam-out, which can help prevent overtightening. Pozidriv resembles Phillips but with additional lines to reduce cam-out further. Torx drives use a six-point star profile, offering higher torque transmission and reduced cam-out. Hex drives use a hexagonal recess, while Robertson or square drives provide strong torque transfer with good bit alignment. There are many specialized or tamper-resistant drives as well, such as Tri-wing or security Torx, used to deter unauthorized disassembly.

Performance characteristics depend on drive geometry, size, and material. Torx and square drives generally deliver greater torque with less cam-out than slotted or Phillips types. Drive compatibility requires matching the bit size to the screw head size; using the wrong size can strip the screw or slip. Standards and sizes vary by region and industry, with common practice aligning tool sets to the dominant drive types in a given application.

In summary, screwdrives define how effectively a screw can be driven and removed, influencing torque capacity, alignment, and ease of use in various applications.