A BT40 pull stud (also called a retention knob) is the part the machine drawbar grips to hold the tool holder in the spindle. Studs are sold in 45, 60 and 90 degree versions, with or without a through hole for coolant. The one you fit must match your machine's drawbar, and the machine manual decides which.
What a pull stud does
The stud screws into the back of the BT40 holder. The drawbar inside the spindle grips the head of the stud and pulls the holder's taper into the spindle. The drawbar is made for one stud shape, so the stud has to be the shape your machine expects.
The types
Choice
Options
What decides it
Head angle
45, 60 or 90 degree
The drawbar of your machine. Read the machine manual or the drawbar drawing
Hole
With hole or without hole
Whether the machine supplies coolant through the spindle
Thread
BT40 studs are listed by makers with an M16 thread
The thread in the back of your holder
Tool catalogues describe BT pull studs under JIS B 6339 (MAS 403 BT). If your manual gives a standard and a type instead of an angle, match that against the stud maker's table before ordering.
With hole and without hole
A stud with a hole lets coolant pass through the centre of the holder, for machines with through-spindle coolant. A stud without a hole is solid.
How to identify the stud you have
Look in the machine manual for the pull stud drawing or part number.
Compare a stud from a holder that already runs in the machine: head angle, overall length and thread.
Do not mix stud types across the holders of one machine.
What to check before you order
The head angle: 45, 60 or 90 degree.
With hole or without hole.
The thread and length your holder takes. Our product page does not state them, so confirm them against your holders.
