Haas SK40/SK50 pull stud (retention knob) for DIN 69871 tool holders, M16/M24 thread, through-bore and O-ring variants

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Haas SK40, for DIN 69871 holders - through bore, M16×2.0, L57.15 mm, angle 45°

Haas SK50, for DIN 69871 holders - M24×3.0, L85.05 mm, angle 45°

Haas SK40, for DIN 69871 holders - through bore, with O-ring, M16×2.0, L57.15 mm, angle 45°

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Product description

Pull stud for Haas SK40 SK50 – geometry selection

1. Pull stud and spindle selection

A pull stud screws into a toolholder. Its head engages the spindle gripping mechanism. Selection requires the complete profile, thread and measurement points to be compared together with the passage and sealing arrangement.

This description presents nominal reference geometry for metric SK40 and SK50 types used in Haas machines. Holder size is one selection parameter; it does not replace the drawing of the required part.

2. Holder designation and stud geometry

DIN 69871 is a designation relating to the toolholder. The holder designation alone does not specify the complete pull-stud profile, bore type or sealing arrangement.

Compare the geometry required by the spindle with the reference below. Matching the thread alone, the SK40 or SK50 name, or one external dimension is not enough to substitute pull studs.

3. Reference nominal dimensions for SK40 and SK50

Use the table to compare with the drawing of the stud required by the machine. These are nominal reference dimensions, not measurements of a specific part. External dimensions do not establish the passage or O-ring type.

Lengths and diameters are in millimetres. TP includes the metric thread and pitch; KA is the angle of the rear gripping surface shown in the drawing.

Size	Thread TP	OAL [mm]	ØK [mm]	ØN [mm]	W [mm]	FE [mm]	FT [mm]	KA
SK40	M16×2.0	57.15	15	10	19	32.1	25.1	45°
SK50	M24×3.0	85.05	23	17	30	45.05	35.05	45°

4. Measurement points: OAL, FE and FT

Symbol	Meaning in the reference geometry
OAL	Overall length from the head front to the end of the threaded portion
ØK	Maximum gripping-head diameter
ØN	Neck diameter below the head
W	Wrench size: width across the flat surfaces
TP	Metric thread designation including pitch
KA	Angle of the rear gripping surface of the head
FE	Head front to the flange support face
FT	Rear boundary of the maximum head diameter to that same flange support face

FE and FT locate the head relative to the flange. FT is not a thread length. Use the points shown in the drawing for both lengths; measuring from another face changes the meaning of the result.

The SK50 service drawing uses the separate designation D = 35.2 mm. FT in this table is 35.05 mm. Do not average or substitute values from these two drawings. Compare the complete drawing and its measurement points for the required type.

5. Standard and TSC — passage comparison

The table compares reference types. It does not assign a passage type to a specific part from the size name alone.

Reference type	Passage path
Standard (Solid)	Without an axial through passage for coolant
TSC	Axial through passage for coolant

The absence of a through passage does not mean there is no bore at all. A part may have a blind or another bore whose path must be identified. A visible opening in the head face alone does not prove a through passage.

For through-spindle coolant, check the passage required by the machine system and its connection to the holder. The external head and neck geometry does not replace identification of the bore path.

6. O-ring and sealing position

The O-ring and coolant passage are separate features. A ring does not establish a through passage, and TSC alone does not specify the number or position of seals.

Compare the required contact position, ring presence and number, and the position of the groove or seal inside a bore. Check sealing separately from the thread, lengths and head angle. The dimension table above does not assign an O-ring to SK40 or SK50.

7. Comparing the required profile

Start with the drawing of the part required by the spindle. Compare in this order:

The metric type and complete thread designation including pitch.
The head diameter ØK, neck diameter ØN and wrench size W.
The overall length OAL and FE/FT distances measured from the correct faces.
The rear gripping-surface angle KA.
The passage path and separate sealing requirements.

The metric designations in this table do not substitute an inch thread in another type. A match in one parameter, such as M16, does not establish the complete profile. Retain the symbols and dimensions of the drawing for the required part.