ISO 1101 GD&T symbols: geometrical characteristics and the tolerance frame

The geometrical characteristics that a tolerance frame can control, with their symbols, the group each belongs to and whether a datum is needed.

ISO 1101:2017, clause 5, Table 2 'Symbols for geometrical characteristics' (characteristic, specification group, datum needed, subclause). datum: 'none' = 'no' in Table 2, 'required' = 'yes', 'optional' = 'no' in one row and 'yes' in another (position; line and surface profile, which have no datum as a form specification and a datum as orientation or location). symbol = MechPilot's Unicode mapping by Unicode character name (Miscellaneous Technical block); the drawn symbol follows the figure in Table 2. nameIt = MechPilot's own translation (UNI EN ISO 1101 Italian terms not seen).

• Line profile: Datum 'no' as form, 'yes' as orientation or location. Called 'profile any line' in former versions (Table 2, NOTE 1).
• Surface profile: Datum 'no' as form, 'yes' as orientation or location. Called 'profile any surface' in former versions (Table 2, NOTE 2).
• Position: Table 2 gives 'no' and 'yes' (see also ISO 5458).
• Circular run-out: Unicode has no dedicated circular run-out character; the ISO symbol is a single filled arrow at about 45 degrees, drawn as a graphic.

Tolerance frame

Frame height H

2 h — Height of frame H = 2h for type B lettering (H 5, 7, 10, 14, 20, 28, 40 for h 2.5, 3.5, 5, 7, 10, 14, 20). Increase it when an additional tolerance value is inscribed in a lower compartment.

Line width d

0.1 h — Thickness of line d = h/10 for type B (0.25 to 2 mm in Table 2), the same as the lettering line width.

Datum target circle diameter

4 h

Source

ISO 7083:1983, clause 5, Table 2 (lettering type B) and 5.2; ISO 1101:2017, clause 5 NOTE refers to ISO 7083 and its own Annex F (not seen) for proportions

Datum indicator

a capital letter in a square frame, connected by a leader to a datum triangle; the triangle may be filled (solid) or open (blank) — ISO 1101:1983, 8.1 (via IS 8000 (Part 1):1985); in ISO 1101:2017 datums are covered by ISO 5459, not seen

Notes from the data file

• Table 2 lists 15 rows; concentricity and coaxiality share one symbol, giving 14 distinct symbols.
• Additional symbols (combined zone CZ, separate zones SZ, unequal zone UZ, projected zone P, MMR M, LMR L and others) are in ISO 1101:2017 Tables 3 and 4 and are not stored here yet.