GB944.1-1985 Standard Screws with Phillips Head

1. Type H Cross Recess (Phillips)

The Type H recess, commonly known as Phillips, is designed with tapered flanks and rounded corners. This geometry intentionally allows the driver to “cam out” (slip out) of the recess when excessive torque is applied, preventing damage to the screw threads or the work surface.

Note 1: For Recess No. 0, angle α is replaced by r(min)=0.25mm, r(max)=0.36mm.
Note 2: Dimensions listed are theoretical values for mold manufacturing and are not typically inspected on the finished product directly.

2. Type Z Cross Recess (Pozidriv)

The Type Z recess, known as Pozidriv, features parallel flanks and additional “tick marks” between the wings. This design eliminates the cam-out effect found in Type H, allowing for higher torque transmission without slippage. It is the preferred choice for high-speed assembly lines.

3. Inspection & Gauging (Type H)

To ensure proper driver engagement, the recess dimensions are verified using standard gauges. The following table provides the critical dimensions for the gauge nibs used to inspect Type H recesses.

4. Ever Power Technical Analysis: H vs. Z

As experts in stainless steel fasteners, we often encounter field failures due to mismatched driver bits. Here is the critical distinction:

• Identification: Type Z (Pozidriv) screws are marked with four distinct radial lines (“tick marks”) between the recess wings. Type H (Phillips) screws have clean corners.
• Compatibility Warning: A Phillips driver will fit loosely in a Pozidriv screw, causing it to round off the corners under torque. Conversely, a Pozidriv driver will not seat fully into a Phillips screw, leading to cam-out and damage.
• Recommendation: For automated assembly where high torque is required, specify Type Z. For consumer goods where preventing overtightening is a safety feature, specify Type H.

Note on Standards: The dimensions in GB 944.1 are theoretical values intended for mold and tool manufacturing. Final product inspection relies on the penetration depth of the gauge, not direct measurement of these angles.