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ASME B47.1-2007 (2012) — Gage Blanks
📐 ASME B47.1-2007 (2012), Gage Blanks, is the authoritative American National Standard for the structural dimensions of gage blanks, whose content base is the American Gage Design Standards (AGD). A “gage blank” is a gage body that has not yet received final precision finishing of its measuring surfaces — manufactured to standard dimensions with stock allowance, ready for the gage maker or metrology laboratory to lap and finish into a final GO/NOT GO gage. The Standard covers blanks for plain cylindrical plug gages, thread plug gages, plain ring gages, thread ring gages, snap gages, flush pin gages, double-end built-up snap gages, flat plug gages, and the Bilock handles for flat plug gages. The 1988 edition was fully revised, issued in 2007, and reaffirmed in 2012. Section 4 of the Standard defines the Official Monogram used to designate products made to the American Gage Design Standards.
💡 The value of standardizing gage blanks is that a given nominal size of GO and NOT GO gage shares one common blank OD, length, and handle geometry: gage makers can produce economically in quantity, and finished gages from different makers match in mounting, gripping, and usage.
1. Scope and General Framework 📌
The Standard is organized in nine sections: Section 1, Scope; Section 2, Terminology; Section 3, Details of Construction — American Gage Design Standards; Section 4, Official Monogram; Section 5, Application of the American Gage Design Standards to Special Types of Gages — Recommended Practice; Section 6, Flush Pin Gages; Section 7, Double-End Built-Up Snap Gages; Section 8, Flat Plug Gages; and Section 9, Handles, Bilock, for Flat Plug Gages. Numerous figures and tables give the construction dimensions of each gage type over its diameter ranges. Plain cylindrical plug gage blanks are split into two diameter segments: above 0.010 in. through 8.010 in., inclusive, and above 8.010 in. Thread plug, plain ring, and thread ring gages each have their own diameter segments and dimensional tables. Thread ring gage blanks, for example, are organized by “Range No.” from 1-T through 12-T, covering thread ring gages from No. 0 through 4-3/4 in., plus fine-pitch instrument thread ring gages, No. 0 through No. 12.
2. Gage Blank Types and Construction 🔧
| Gage Type | Blank Construction | Size Range Covered |
|---|---|---|
| Plain cylindrical plug gage | Working section + shank (may take a handle) | 0.010–8.010 in.; above 8.010 in. |
| Thread plug gage | Thread-section blank + square/round shank | Segmented by thread size |
| Plain ring gage | Ring blank; bore left with lapping stock | Segmented by bore size |
| Thread ring gage | Ring blank; thin or thick types | No. 0 – 4-3/4 in.; fine-pitch instrument No. 0 – 12 |
| Snap gage | Bow frame + anvils | Double-end built-up type |
| Flat plug gage | Flat-blade measuring faces | With Bilock handles |
| Flush pin gage | Pin flush with a reference surface | Depth/step checking |
Taking the thread ring gage blank as an example, the Standard gives, for each range number, the assembly size, ring outside diameter, thickness (with the thin/thick selection rule), ream size, drill size, and the minimum/maximum pitch diameter of the corresponding thread. The general notes specify that all NOT GO thread ring gages are to use thin blanks, while GO ring gages use thin or thick blanks by diameter and pitch: from No. 0 to 1/2 in. inclusive, all pitches use thin blanks; above 1/2 to 1-1/8 in., pitches of 12 TPI and finer use thin and coarser pitches use thick; above 1-1/8 in., pitches of 10 TPI and finer use thin and coarser pitches use thick.
⚠️ The thin/thick choice for GO and NOT GO ring blanks is not arbitrary: a thicker blank is stiffer and lasts longer, but it lengthens the engagement and can distort judgment on short threaded parts. Follow the diameter–pitch rule in the notes or the gage verdict may be unreliable.
3. Representative Thread Ring Gage Blank Dimensions 📏
| Range No. | Diameter Range (in.) | Assembly Size | Ring OD | Example Thread |
|---|---|---|---|---|
| 1-T | No. 0 through 0.059 | 1-1/4 | about 3/4 | 0.164-36 fine |
| 2-T | 1/4–5/16 | 1-3/8 | about 13/16 | 0.216-28 |
| 3-T | 3/8–1/2 | 1-3/4 | about 1 | 0.250-28 |
| 4-T | 9/16–3/4 | 2-3/16 | about 1-1/8 | 0.3125-24 |
| 6-T | 1-1/4–1-1/2 | 3-1/4 | about 1-1/2 | 0.4375-20 |
| 8-T | 2-1/8–2-1/2 | 4-1/2 | about 1-7/8 | 0.500-20 |
| 11-T | 3-5/8–4 | 6-3/8 | about 2-1/2 | 0.625-18 |
| 12-T | 4-1/8–4-3/4 | 7-1/4 | about 2-3/4 | 0.625-18 |
4. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: determine the nominal size and tolerance zone of the part → choose the gage type (plug / ring / snap) → look up the blank by diameter segment and range number → decide GO/NOT GO and thin/thick → finish and lap the measuring surfaces.
- 🔧 Blank vs. finished gage: tabulated blank dimensions are the body dimensions; measuring surfaces (bore, OD, threads) keep lapping/finishing stock. The drill and ream sizes given by the Standard are the lead-in dimensions before final machining.
- 📊 Material and heat treatment: gage blanks are commonly made of tool steel, hardened for wear resistance and dimensional stability; precision gages also receive sub-zero treatment and aging to relieve residual stress.
- 📋 Official Monogram: gages made to the American Gage Design Standards may carry the Official Monogram per Section 4 as a conformity mark — check it in purchasing and acceptance.
- ✅ Special gages: Section 5 recommends how to apply AGD designs to special gage types; for example, special thicker blanks are sometimes required to check long lengths of engagement or exceptionally coarse pitch threads.
🚨 A gage is a measuring instrument, not an ordinary part: dimensional errors, bad heat treatment, or over-lapping at the blank stage translate directly into measurement error. All finishing and acceptance must be traceable to standard gages or gage blocks; never “patch to size” on a blank.
5. Frequently Asked Questions ❓
❓ Q: How do B47.1 and AGD (American Gage Design) relate?
A: B47.1 is the current vehicle of the AGD standards: Section 3, Details of Construction, is the AGD content defining unified structural dimensions for gage blanks and finished gages, and AGD-conformant products may bear the Official Monogram of Section 4.
A: B47.1 is the current vehicle of the AGD standards: Section 3, Details of Construction, is the AGD content defining unified structural dimensions for gage blanks and finished gages, and AGD-conformant products may bear the Official Monogram of Section 4.
❓ Q: Why must NOT GO thread ring gages use thin blanks?
A: A NOT GO gage should engage only a limited number of turns (usually no more than about three); an over-thick blank lengthens engagement and can amplify small pitch errors into a wrong verdict. GO gages choose thin or thick by the diameter–pitch rule.
A: A NOT GO gage should engage only a limited number of turns (usually no more than about three); an over-thick blank lengthens engagement and can amplify small pitch errors into a wrong verdict. GO gages choose thin or thick by the diameter–pitch rule.
❓ Q: Are blank dimensions the finished gage dimensions?
A: No. Blank dimensions are body dimensions; the measuring surfaces still carry lapping/finishing stock, and the drill and ream sizes are lead-in dimensions. Finished tolerances are set by the applicable gage tolerance standards (e.g., B1.2 for thread gages).
A: No. Blank dimensions are body dimensions; the measuring surfaces still carry lapping/finishing stock, and the drill and ream sizes are lead-in dimensions. Finished tolerances are set by the applicable gage tolerance standards (e.g., B1.2 for thread gages).
🔍 Q: How do I choose the Bilock handle for a flat plug gage?
A: Section 9 specifies Bilock handle dimensions, matched to the flat plug gage size and measuring-face geometry, to give firm clamping, correct positioning, and clearance from the workpiece.
A: Section 9 specifies Bilock handle dimensions, matched to the flat plug gage size and measuring-face geometry, to give firm clamping, correct positioning, and clearance from the workpiece.
