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ASME B107.31M-1997 — Cross Tip Screwdrivers Gaging
📏 ASME B107.31M-1997 is a standard in the ASME B107 family, Hand Tools and Accessories, that defines the dimensional and functional characteristics of gaging for cross tip screwdrivers — the system of gages used to verify Phillips (PH) and Pozidriv (PZ) screwdriver tips. It works hand in hand with ASME B107.30 (Cross Tip Screwdrivers): B107.30 defines the product dimensions and performance, while B107.31M provides the gages and gage size tables needed to accept those characteristics. It is the technical basis for manufacturer outgoing inspection, buyer incoming acceptance, and third-party conformance assessment.
💡 Gages turn invisible tolerances into visible verdicts: a complete gaging system lets an inspector confirm tip wing spread, angles, and penetration depth in seconds without expensive metrology equipment.
1. Scope and Composition of the Gaging System 📌
The Standard defines a complete system of gages for inspecting cross tip screwdrivers, grouped by function:
- Dimensional gages: verify tip wing spread and profile, including the Style A Ring Gage and the Master Plug Gage.
- Functional gages: verify penetration depth and engagement in a simulated recess, including the Style B GO/NO-GO Ring Penetration Gage and the Penetration Gage Assembly.
- Support accessories: the Anvil and Spacer, which support the shank and control the inspection position for repeatable results.
| Gage | Applicable Tips | Function |
|---|---|---|
| Style A Ring Gage | PH 1–4, PH 0, PZ sizes | Check profile and dimensions of the main/minor wing spread |
| Master Plug Gage | PH 1–4, PH 0, PZ sizes | Reference master used to verify the ring gages themselves |
| Style B GO/NO-GO Ring Penetration Gage | PH 1–4, PH 0, PZ sizes | Judge whether tip penetration in a simulated recess is acceptable |
| Penetration Gage Assembly + anvil/spacer | All cross tip screwdrivers | Support the shank and measure overall assembly length and insertion limit |
2. Gage Dimensional and Tolerance Requirements 📏
The Standard tabulates the key geometry of each gage:
- Anvil and spacer dimensions: governing the support surface diameter and spacer thickness so the shank is supported reliably and the inspection position is consistent.
- Style A ring gage dimensions: slot width, depth, and angle parameters for PH sizes 1–4, size 0, and the PZ sizes, establishing the intended fit relationship with the tip.
- Driver penetration limits: minimum and maximum insertion depth of the tip in the gage recess, preventing tips that are too short (poor engagement) or too long (bottoming out).
⚠️ Gages are not ordinary fixtures — they act as the “agreed reference” of the acceptance chain. If a ring gage wears or is damaged, the whole verification chain is distorted. Gages should be periodically checked against the master plug gage, and damaged gages must never be repaired informally and returned to service.
3. How the Gaging System Works 🔬
A cross tip screwdriver tip is a tapered four-flute (plus PZ secondary flutes) profile whose form errors are hard to measure directly with calipers. The gaging system works on the comparison principle:
- Profile comparison: the tip is inserted into the simulated recess of a Style A ring gage; a conforming tip fits with no obvious play — oversize wings prevent insertion, undersize wings show visible looseness.
- Functional simulation: the Style B GO/NO-GO ring penetration gage simulates the depth and shape of a screw recess; “the GO end should pass, the NO-GO end should stop” judges whether penetration depth is acceptable.
- Traceability: master plug gages are made to the nominal dimensions of the Standard and are used periodically to monitor ring gage wear, keeping gage accuracy traceable.
4. Engineering Practice and Application Notes 🛠️
- 🔍 Outgoing inspection: manufacturers should incorporate the gaging system into outgoing inspection, checking tip wing spread and penetration on every driver.
- 🔧 Incoming acceptance: buyers can perform sampling or 100% inspection with standard gages and sign supply agreements based on B107.31M acceptance, reducing disputes over defective tips.
- 📊 Gage management: keep an inventory with serial numbers and verification intervals, check against master plug gages, record the results, and store gages in dedicated anticorrosion, impact-protected cases.
- 📋 Pairing with B107.30: the gage dimensions echo the tip dimensions and test-block wing spread of B107.30; procurement and acceptance documents should cite both standards together.
🚨 Tip geometry failure is the root cause of “looks usable but actually slips”: undersize wings cause cam-out that damages screw recesses during tightening, while oversize wings will not enter the slot or bind. Any tip that fails inspection must be rejected.
5. Frequently Asked Questions ❓
❓ Q: What is the difference between a ring gage and a master plug gage?
A: The Style A ring gage is the working gage that checks tips; the master plug gage is the reference (“master”) used to verify wear of the ring gage itself. They play different roles in production inspection and gage management.
A: The Style A ring gage is the working gage that checks tips; the master plug gage is the reference (“master”) used to verify wear of the ring gage itself. They play different roles in production inspection and gage management.
❓ Q: Why are separate gages provided for PH size 0 and PH sizes 1–4?
A: PH 0 is a miniature tip whose recess size and fit differ from the larger sizes, so the Standard gives separate gage dimensions. Always use the gage matching the tip size — never mix sizes.
A: PH 0 is a miniature tip whose recess size and fit differ from the larger sizes, so the Standard gives separate gage dimensions. Always use the gage matching the tip size — never mix sizes.
❓ Q: What does a failed GO/NO-GO penetration check indicate?
A: It indicates the tip form (taper, wing spread, or angle) does not match the recess defined by the Standard, so engagement in actual use is insufficient or excessive, risking slippage or damage to the screw; the tip must be rejected and the process adjusted.
A: It indicates the tip form (taper, wing spread, or angle) does not match the recess defined by the Standard, so engagement in actual use is insufficient or excessive, risking slippage or damage to the screw; the tip must be rejected and the process adjusted.
🔍 Q: Do the gages need periodic calibration?
A: Yes. Working gages wear and should be checked periodically against master plug gages with records kept; the interval depends on usage frequency, typically at least annually, and shorter when used heavily.
A: Yes. Working gages wear and should be checked periodically against master plug gages with records kept; the interval depends on usage frequency, typically at least annually, and shorter when used heavily.
