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ASME B107.17-2015 — Gages and Mandrels for Wrench Openings
📏 ASME B107.17-2015 is the dedicated standard for gages and mandrels used to inspect wrench openings within the ASME B107 family of standards for hand tools and accessories. It specifies the dimensions, tolerances, material, and hardness requirements of gages and mandrels used to verify the openings of open-end wrenches, box wrenches, combination wrenches, and socket-type wrenches. The Standard provides a unified, traceable set of inspection instruments that support conformity assessment of wrench openings — serving as the companion metrology standard for the various wrench standards in the B107 series (such as B107.1, B107.100, and B107.110).
💡 Conformity of a wrench opening cannot be established by eyeballing or casual caliper measurement. B107.17 converts “is the opening in tolerance?” into an objective GO/NO-GO verdict, ensuring consistent results across factories and production lots.
1. Scope and General Framework 📌
The wrench opening is the critical interface with the fastener head: an oversized opening slips and damages the hex, while an undersized opening will not fit. B107.17 provides standardized inspection means:
- Gages: GO/NO-GO gages for checking open-type openings (e.g., open-end wrench jaws), typically made as paired “GO” and “NO-GO” members.
- Mandrels: inspection mandrels for closed-type openings (hex or twelve-point sockets of box wrenches), whose across-corners and across-flats dimensions are designed to the tolerance band.
The Standard applies to in-line inspection, final inspection, and third-party acceptance of products made to the applicable ASME B107 wrench standards, and it is an indispensable metrology foundation of wrench manufacturing quality systems. Results support not only individual go/no-go decisions but also statistical process control (SPC) for monitoring opening-machining stability.
⚠️ B107.17 provides “inspection tools,” not “design drawings”: the gage and mandrel tolerance bands must be coordinated with the opening tolerances of the respective wrench standard. Always confirm the corresponding wrench standard and size series before selecting gages — mismatched gages give misleading verdicts.
2. Classification of Gages and Mandrels 🔩
The Standard classifies gages and mandrels by the opening type they inspect:
- Open-End Wrench Gages: for checking the width and depth of open-end wrench jaws; typically flat GO/NO-GO gages — the GO member slips in, the NO-GO member must not.
- Box Wrench Mandrels: for checking hex or twelve-point closed openings, verifying that across-flats and across-corners diameters fall within the tolerance band.
- Combination Wrench Gages/Mandrels: covering both ends (open end and box end) of combination wrenches.
- Socket and Drive-Accessory Gages: for verifying socket bores and square-drive engagement dimensions.
This classification lets manufacturers select the matching inspection tool for each product type and lets metrology departments maintain gage inventory records accordingly.
3. Technical Requirements and Specifications 📊
As measuring instruments, gages and mandrels must be more accurate than the tolerances they inspect. Typical requirements of the Standard are summarized below:
| Parameter | Typical Requirement | Remarks |
|---|---|---|
| Dimensional tolerance | Working size narrowed by about 10%–20% of the inspected opening tolerance | Ensures reliable verdicts and avoids boundary disputes |
| Across-flats / across-corners | Hex and twelve-point mandrels made to the standard size series | Matched to wrench sizes (e.g., 1/4 in, 3/8 in, 10 mm) |
| Material | Tool steel or alloy steel, hardened and stabilized | Wear resistance and long-term dimensional stability |
| Hardness | Working surfaces about Rockwell C (RC) 60 | Wear resistance and deformation resistance |
| Surface finish | Working surfaces precision-ground to the specified Ra | Surface defects must not affect measurement |
| Marking | Size designation, maker, and gage control number | Traceability and metrology management |
Dimensions are provided in both SI (mm) and U.S. Customary (in.) units to serve both markets. The Standard also addresses gage wear evaluation and repair: when wear approaches the judgment boundary, the gage shall be recalibrated and replaced as appropriate to keep results reliable over the long term.
🚨 Gage wear is a hidden risk in inspection: frequently used GO gages can wear “loose” and pass out-of-tolerance parts. Gages must be recalibrated on a defined schedule with records retained — never use the same gage indefinitely.
4. Engineering Practice Essentials 🛠️
- 🔍 Inspection workflow: confirm the wrench standard and size; select the matching gage; use the GO member to check the lower limit and the NO-GO member to check the upper limit — GO passes and NO-GO fails means acceptable.
- 📅 Metrology management: maintain gage and mandrel inventory with a periodic calibration schedule set by usage frequency; affix validity labels after successful calibration.
- ⚠️ Usage method: slide gages into the opening gently — never force them with blows; clean the gage and workpiece surfaces before inspection to avoid chips and oil affecting the verdict.
- 📊 Data analysis: aggregate inspection results by lot, monitor opening-size distributions to detect tool wear or fixture drift, and act early via SPC.
- 📋 Procurement acceptance: require calibration certificates from gage suppliers (traceable to national or international standards) to ensure the gages themselves are valid.
5. Frequently Asked Questions ❓
❓ Q: Why not simply measure wrench openings with a caliper?
A: Caliper measurement is affected by measuring force, angle, and operator; open and closed opening geometries differ. GO/NO-GO gages and mandrels judge against the tolerance band — simple, objective, consistent, and ideal for batch inspection and acceptance.
A: Caliper measurement is affected by measuring force, angle, and operator; open and closed opening geometries differ. GO/NO-GO gages and mandrels judge against the tolerance band — simple, objective, consistent, and ideal for batch inspection and acceptance.
❓ Q: What does it mean if both the GO and the NO-GO members fit?
A: The opening is oversized (above the upper limit) and the wrench is unacceptable. If the NO-GO member enters, the across-flats dimension exceeds the maximum allowed and the wrench may slip on the fastener.
A: The opening is oversized (above the upper limit) and the wrench is unacceptable. If the NO-GO member enters, the across-flats dimension exceeds the maximum allowed and the wrench may slip on the fastener.
❓ Q: How many gages does one wrench size need?
A: Per the Standard’s classification, usually a paired set: one GO and one NO-GO (or the corresponding GO/NO-GO mandrel), i.e., two members; configure gage sets per the size series of your product range.
A: Per the Standard’s classification, usually a paired set: one GO and one NO-GO (or the corresponding GO/NO-GO mandrel), i.e., two members; configure gage sets per the size series of your product range.
🔍 Q: How is the gage calibration interval determined?
A: By usage frequency, gage material, and wear rate. Frequently used GO gages need shorter intervals (e.g., monthly or quarterly); lightly used ones may extend to yearly. Adjust intervals using wear trends from calibration records.
A: By usage frequency, gage material, and wear rate. Frequently used GO gages need shorter intervals (e.g., monthly or quarterly); lightly used ones may extend to yearly. Adjust intervals using wear trends from calibration records.
