15. Bored hole size before tapping ( for thread cutting )
■ Recommended Bored Hole Size Table for Taper Pipe Threads (PT) (refer to JIS B 0203) Production data
・PT internal threads have R design on their crests. The taps should cut threads with their thread root.
・On thread having non-full threads, if you are going to cut effective thread length ℓ, use the tap of long type.
unit: mm
Thread Standards Minor Diameter Recommended Bored reference
When When Hole Sizes (reference) Tap
Basic Effective Thread Length Threads Threads
Basic Diameter (Minimum) Pipe End have do not have Maximum Size of Straight Basic Diameter
Diameter Position (Workpiece non-Full the non-Full Bored Hole Position,
Size Face) Threads Threads ℓg
Pipe End When When (Basic Position Position
Threads Threads Diamater ) away from away from When When
Tolerance Tolerance in have do not have Pipe End by Pipe End by Threads Threads Long Short
in radial axial non-Full the non-Full ℓ t have do not have Thread Thread
direction direction Threads1) Threads1) non-Full the non-Full Type Type
c ℓ t Basic Size Basic Size Basic Size Threads Threads
① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩ ⑪ ⑫
PT 1/16 - 28 ± 0.071 ± 1.13 6.2 4.4 6.561 6.174 6.286 6.1 6.2 13.0 10.5
PT 1/8 - 28 ± 0.071 ± 1.13 6.2 4.4 8.566 8.179 8.291 8.1 8.2 13.0 10.5
PT 1/4 - 19 ± 0.104 ± 1.67 9.4 6.7 11.445 10.858 11.026 10.7 10.9 21.0 12.5
PT 3/8 - 19 ± 0.104 ± 1.67 9.7 7.0 14.950 14.344 14.513 14.2 14.4 21.0 14.0
PT 1/2 - 14 ± 0.142 ± 2.27 12.7 9.1 18.631 17.837 18.062 17.6 17.9 25.0 17.0
PT 3/4 - 14 ± 0.142 ± 2.27 14.1 10.2 24.117 23.236 23.480 23.0 23.3 25.0 19.0
PT 1 - 11 ± 0.181 ± 2.89 16.2 11.6 30.291 29.279 29.566 29.0 29.3 32.0 22.0
PT 1 1/4 - 11 ± 0.181 ± 2.89 18.5 13.4 38.952 37.796 38.115 37.6 37.9 32.0 24.5
PT 1 1/2 - 11 ± 0.181 ± 2.89 18.5 13.4 44.845 43.689 44.008 43.5 43.8 32.0 25.5
PT 2 - 11 ± 0.181 ± 2.89 22.8 16.9 56.656 55.231 55.600 55.0 55.4 35.0 28.0
Note 1) Length toward End of Smaller Diameter from Baisc Diameter Position
When Threads have When Threads do not have
non-Full Threads the non-Full Threads
⑥ Basic Diameter Position ⑥
Remarks 1. Opening of Internal Thread (Face of workpiece) is Basic
⑤t Diameter Position.
Remarks 2. Effective Thread Length has 2 types, with non-Full Thread
④ Type and without non-Full Thread Type.
⑦ Remarks 3. Concerning bored hole shape, considering load on taps,
⑧ taper bored hole is recommended.
Remarks 4. When applying taper bored hole, by referring to values
shown in columns ②·⑥~⑧, prepare the taper hole by
using pipe reamer (1/16 taper). By referring to values
shown in columns ⑨ and ⑩, select the drill diameter
before reaming by taking reamer's margin into account.
Remarks 5. When preparing straight bored hole, by referring to
values shown in columns ⑨ and ⑩, select drill diameter.
Information Technical
Technical-42
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