Don't be embarrassed!! I usually see this as "guide (hole)" but there seem to be several names.... A Google search confirms it's not that common...

datum 基準点 | 既知数 | 事項 | 資料 | 統計
datum 基準面 | 基準
datum データ | データム | 基準 | 測地原点 | 与件
Datum 基準線
datum データム | データ項目 | 基準 | 基準線 | 基準面 | 資料 | 測地基準線 | 測地系 | 測地原点 | 与件
datum A 基準A
datum pin 基準ピン
datum line 水準線 | 基準線 | 基本水準線
datum line データムライン | データム線 | 基準のレベル | 基準線 | 基準面 | 基本水準線 | 基本水準面 | 水準線
datum line 基準線

Drafting Standards & GD&T - Do I double the result?
The datum hole is located exactly in its correct position, by definition. The second hole is located with respect to the datum hole. The 0.1 value is a diameter around the nominal position of the second hole. ...
www.eng-tips.com/viewthread.cfm?qid=130692&page=10 - 28k - Cached - Similar pages

[PDF] 8 mm Wide Magnetic Tape Cartridge for Information Interchange ...
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Plane Y is perpendicular to Plane X and Plane Z and passes through the centre of Datum Hole A. ... The centre of the circular datum hole A shall be at the intersection of planes X and Y (see figure 10). ...
www.ecma-international.org/publications/files/ECMA-ST/Ecma-... - Similar pages

NC ROTARY TABLE KITAGAWA MRM
Datum-Hole Diameter dia.(mm), dia.32, dia.40, dia.45. Gear ratio, 1/60, 1/72, 1/90. Clamping Torque(N·m) (Pneumatic 0.5MPa), 150, 310, 350. Max. Work Piece Inertia kgm2(kgf.cm.sec2), 0.22/2.2, 0.51/5.2, 1.00/10.2 ...
kiw.co.jp/wpage/mtools/nct_mr_e.html - 23k - Cached - Similar pages

[PDF] 12.65-mm Type D-11 Format
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Datum plane X shall be orthogonal to datum plane Z and shall include the centers of datum holes (a) and. (b). Datum plane Y shall be orthogonal to both datum plane X and datum plane Z and shall include the. center of datum hole (a) as ...
bssc.sel.sony.com/BroadcastandBusiness/minisites/cinealta/docs/S368M.pdf - Similar pages