GB 944.1-1985: Cross Recesses for Screws Standard
Introduction
This standard, GB 944.1-1985, specifies the dimensions and requirements for cross recesses used in screws, including Phillips-type designs. Cross recesses are essential in fastening applications, providing improved torque transmission and reduced cam-out compared to slotted drives. They are widely applied in industries such as automotive, electronics, and machinery manufacturing.
GB 944.1-1985 defines two primary types: H-type and Z-type cross recesses, suitable for various screw sizes from recess No. 0 to No. 4. This standard ensures compatibility between screws and drivers, minimizing assembly errors and enhancing product reliability.
The standard is applicable to machine screws, self-tapping screws, and wood screws, with dimensions provided as theoretical values for mold manufacturing. Actual products are not inspected against these exact values, but they guide production to achieve consistent performance.
GB 944.1-1985 Standard Overview
Released in 1985 by the Standardization Administration of China, GB 944.1-1985 has not undergone major revisions and remains a reference for cross recess specifications. It aligns with international standards like ISO 4757:1983, which also defines H-type and Z-type recesses.
The scope includes dimensions for recesses in screws, gauge head sizes for inspection, and notes on application. It covers recess numbers 0 through 4, focusing on parameters like width, depth, and angles to ensure proper engagement with screwdrivers.
Main content includes detailed tables for H-type and Z-type recesses, along with gauge dimensions for quality control.
Basic Principles of Cross Recesses
Cross recesses are designed with intersecting slots forming a cross shape, allowing for better grip and torque application. The H-type features a standard Phillips design with flared wings, while the Z-type (Pozidriv) has additional ridges for enhanced drive engagement, reducing slippage.
The principle involves precise geometry to balance strength, manufacturability, and performance. Key parameters include slot width (b), penetration depth (e, f), wing span (g), radii (r), and angles (α, β) to optimize force distribution.
Specifications for H-Type Cross Recesses
The H-type cross recess is specified for standard applications. Dimensions are theoretical for mold design.
| Paramètre | 0 | 1 | 2 | 3 | 4 | |
|---|---|---|---|---|---|---|
| b Nominal=Max | b | 0.61 | 0.97 | 1.47 | 2.41 | 3.48 |
| Min | 0.58 | 0.94 | 1.44 | 2.38 | 3.45 | |
| e Min | et | 0.26 | 0.41 | 0.79 | 1.98 | 2.39 |
| Max | 0.36 | 0.46 | 0.84 | 2.03 | 2.44 | |
| g Nominal=Min | g | 0.81 | 1.27 | 2.29 | 3.81 | 5.08 |
| Max | 0.86 | 1.32 | 2.34 | 3.86 | 5.13 | |
| f Min | f | 0.31 | 0.51 | 0.66 | 0.79 | 1.19 |
| Max | 0.36 | 0.56 | 0.74 | 0.86 | 1.27 | |
| r Nominal | r | 0.3 | 0.5 | 0.6 | 0.8 | 1 |
| t1 Reference | t1 | 0.22 | 0.34 | 0.61 | 1.01 | 1.35 |
| α Nominal=Max① | α | / | 138° | 140° | 146° | 153° |
| Min① | / | 137°45′ | 139°45′ | 145°45′ | 152°45′ | |
| β Nominal=Min | β | 7° | 7° | 5°45′ | 5°45′ | 7° |
| Max | 7°15′ | 7°15′ | 6° | 6° | 7°15′ | |
① For recess No. 0, α is replaced by r(min)=0.25mm, r(max)=0.36mm. All dimensions are in mm and theoretical for mold use.
Specifications for Z-Type Cross Recesses
The Z-type offers improved performance with additional features to prevent cam-out.
| Paramètre | 0 | 1 | 2 | 3 | 4 | |
|---|---|---|---|---|---|---|
| b Nominal=Max | b | 0.76 | 1.27 | 1.83 | 2.72 | 3.96 |
| Min | 0.71 | 1.22 | 1.78 | 2.67 | 3.91 | |
| f Nominal=Max | f | 0.48 | 0.74 | 1.03 | 1.42 | 2.16 |
| Min | 0.455 | 0.715 | 1.005 | 1.395 | 2.135 | |
| g Nominal=Max | g | 0.86 | 1.32 | 2.34 | 3.86 | 5.08 |
| Min | 0.81 | 1.27 | 2.29 | 3.81 | 5.03 | |
| r1 Max | r1 | 0.3 | 0.3 | 0.38 | 0.51 | 0.64 |
| r2 Max | r2 | 0.1 | 0.13 | 0.15 | 0.25 | 0.38 |
| j Max | j | 0.13 | 0.15 | 0.15 | 0.2 | 0.2 |
| α Nominal=Min | α | 7° | 7° | 5°45′ | 5°45′ | 7° |
| Max | 7°15′ | 7°15′ | 6° | 6° | 7°15′ | |
| β Nominal=Max | β | 7°45′ | 7°45′ | 6°20′ | 6°20′ | 7°45′ |
| Min | 7°30′ | 7°30′ | 6°5′ | 6°5′ | 7°30′ | |
| γ Nominal=Max | γ | 4°23′ | 4°23′ | 3° | 3° | 4°23′ |
| Min | 4°8′ | 4°8′ | 2°45′ | 2°45′ | 4°8′ | |
| δ Nominal=Max | δ | 46° | 46° | 46° | 56°15′ | 56°15′ |
| Min | 45°53′ | 45°53′ | 45°53′ | 56°8′ | 56°8′ | |
All dimensions are in mm and theoretical for mold use.
H-Type Cross Recess Gauge Head Dimensions
Gauges ensure recess conformity during quality checks.
| Paramètre | 0 | 1 | 2 | 3 | 4 | |
|---|---|---|---|---|---|---|
| b Nominal=Max | b | 0.64 | 1.001 | 1.539 | 2.497 | 3.574 |
| Min | 0.615 | 0.976 | 1.514 | 2.472 | 3.549 | |
| g Nominal=Min | g | 0.813 | 1.27 | 2.286 | 3.81 | 5.08 |
| Max | 0.838 | 1.295 | 2.311 | 3.835 | 5.105 | |
| d Nominal=Min | d | 0.25 | 0.38 | 0.38 | 0.38 | 0.38 |
| Max | 0.38 | 0.51 | 0.51 | 0.51 | 0.51 | |
| e Nominal=Max | et | 0.315 | 0.513 | 1.102 | 2.098 | 2.738 |
| Min | 0.29 | 0.488 | 1.077 | 2.073 | 2.713 | |
| f Nominal=Max | f | 0.31 | 0.51 | 0.64 | 0.79 | 1.12 |
| Min | 0.25 | 0.45 | 0.58 | 0.73 | 1.06 | |
| L Min | L | 3.17 | 3.17 | 4.78 | 7.14 | 8.74 |
| α Nominal=Min① | α | / | 138° | 140° | 146° | 153° |
| Max① | / | 138°15′ | 140°15′ | 146°15′ | 153°15′ | |
| β Nominal=Min | β | 7° | 7° | 5°45′ | 5°45′ | 7° |
| Max | 6°45′ | 6°45′ | 5°30′ | 5°30′ | 6°45′ | |
① For recess No. 0, α is replaced by r = 0.25 ± 0.025mm. All dimensions in mm.
GB 944.1-1985 Standard’s Influence on Industry
This standard standardizes cross recess designs, aiding in global trade and interoperability. It impacts quality control by providing benchmarks for manufacturing, reducing defects in assembly lines. In automotive applications, it ensures reliable fastening; in electronics, it supports miniature screws with precise torque control.
Foire aux questions
What is the difference between H-type and Z-type cross recesses?
H-type is the standard Phillips recess with flared wings for general use, while Z-type (Pozidriv) includes secondary ridges for better grip and reduced cam-out in high-torque applications.
How do I select the appropriate recess number for a screw?
Choose based on screw diameter: No. 0 for small screws (e.g., M1.6), up to No. 4 for larger ones (e.g., M10). Refer to compatible standards like GB/T 845 for specific pairings.
Are these dimensions mandatory for production?
No, they are theoretical for mold manufacturing. Finished products are inspected using gauges, not direct measurement against table values.
What is the purpose of the gauge head dimensions?
Gauges verify recess conformity, ensuring screws fit drivers properly and meet performance requirements during quality assurance.
How does GB 944.1-1985 relate to international standards?
It corresponds to ISO 4757:1983, facilitating international compatibility in screw designs and tooling.
What materials are suitable for screws with these recesses?
Commonly steel, stainless steel, or brass, ensuring the material’s hardness allows for precise recess forming without deformation.
