Guide
ISO 7388-3 Pull Stud Forms: JD, JF, AD, AF, UD and UF Explained
ISO 7388-3 is the pull stud (retention knob) standard for steep-taper tool holders; ISO 7388-1 and ISO 7388-2 cover the shanks. Its form names tell you which older standard a stud matches and whether it has a coolant hole. This guide maps them to MAS-BT, DIN 69872, ANSI/ASME B5.50 and the withdrawn IS 11173-2.
Last updated 29 October 2026
What do the letters in JD, JF, AD, AF, UD and UF mean?
The first letter is the pull stud family the form matches; the second says whether the stud has a coolant hole.
| Letter | Meaning | Pull studs |
|---|---|---|
| J | MAS-BT form (MAS 403 / JIS B6339) | MAS-BT pull studs |
| A | DIN 69872 form | DIN 69872 pull studs |
| U | ANSI/ASME B5.50 form | ANSI retention knobs |
| D | Drilled: with a coolant hole | – |
| F | Solid: no coolant hole | – |
Which ISO 7388-3 form matches which pull stud?
As printed in the PTP catalogue's standard line for each family.
| ISO 7388-3 form | Matches | Formerly IS 11173-2 | Head angle | Tapers | PTP pull studs |
|---|---|---|---|---|---|
| JD / JF | MAS-BT (MAS 403), JIS B6339 | Types 3, 4 and 5 | 60°, 45° and 90° | BT30–BT50 | MAS-BT pull studs |
| UD / UF | ANSI/ASME B5.50 | Type 2 | 45° | CAT30–CAT60 | ANSI retention knobs |
| AD / AF | DIN 69872 | – | 15° | SK30–SK50 | DIN 69872 pull studs |
PTP's JIS B6339 pull studs (15° head) and its ISO 7388/2 pull studs are listed to ISO 7388-3:2016(E) without a form letter. The MG MEGA Strength pull studs have the same dimensions as the equivalent MAS-BT studs.
What were the IS 11173-2 types?
IS 11173-2 has been withdrawn and replaced by IS/ISO 7388-3. The PTP catalogue still prints the old type numbers in each family's standard line.
| IS 11173-2 | Head angle | Today | PTP code |
|---|---|---|---|
| Type 1 | 15° | ISO 7388/2 type A | PSI1A… (ISO pull studs) |
| Type 2 | 45° | ANSI/ASME B5.50 (ISO 7388-3 UD/UF) | PSAN… (ANSI) |
| Type 3 | 60° | MAS-BT (ISO 7388-3 JD/JF) | PSI3B… (MAS-BT 60°) |
| Type 4 | 45° | MAS-BT (ISO 7388-3 JD/JF) | PSI4B… (MAS-BT 45°) |
| Type 5 | 90° | MAS-BT (ISO 7388-3 JD/JF) | PSI5B… (MAS-BT 90°) |
Where can I see every stud of one form?
The taper pages list every PTP pull stud for one spindle taper, with its head angle, thread and coolant hole.
Questions about ISO 7388-3 forms
What does JD mean on a pull stud?
JD is the ISO 7388-3 form of a MAS-BT pull stud with a coolant hole (D = drilled); JF is the same form, solid (F). MAS-BT pull studs retain BT tool holders (MAS 403).
Is a DIN 69872 pull stud ISO 7388-3 form AD or AF?
PTP's DIN 69872 pull studs are listed as ISO 7388-3 forms AD (drilled) and AF (solid). They have a 15° head and retain SK (DIN 69871) tool holders.
Which ISO 7388-3 form is an ANSI CAT40 retention knob?
An ANSI/ASME B5.50 retention knob is ISO 7388-3 form UD (drilled) or UF (solid), formerly IS 11173-2 Type 2. PTP makes the CAT40 size with a 45° head and a 5/8" or M16 thread.