Selling Points of Retention Knob (Pull Stud)

1. High-strength alloy steel & excellent fatigue resistance (Core Selling Point)Made of premium alloy steel such as 20CrMnTi with carburizing & quenching heat treatment. High tensile strength, resistant to cyclic load during ATC tool change, less risk of fracture for safe machining.

2. Precision machined for stable clamping & low runoutPrecision ground ball taper and thread with tight tolerance. Ensures firm fit between tool holder and spindle, reduces radial runout & cutting chatter, improves workpiece accuracy and surface finish.

3. Protects spindle gripper, cuts maintenance costServes as sacrificial wear part to prevent damage to costly spindle grippers, saving expensive spindle repair.

4. Full specifications & wide compatibilityAvailable for BT30/BT40/BT50, CAT, ISO, MAS403, Mazak standards. 45°/60°/90° angles optional. Standard, through-coolant and extended types fit most CNC machining center tool holders.

5. Through-coolant option for better cooling & chip removalCoolant-through pull studs deliver high-pressure coolant straight to cutting zone, improves chip evacuation and extends tool life, ideal for deep hole & high-speed finishing.

6. Wear & corrosion resistance, long service lifeBlack oxide / hardened surface treatment, anti-rust and resistant to cutting fluid, stable in harsh workshop environment with chips and coolant.

7. Safe locking, prevents tool holder ejectionSecurely locks tool holders, avoids loosening under high-speed and heavy cutting, eliminates risks of tool flying out.

8. Cost-effective & easy replacementLow-cost consumable for tool holders, simple installation & stocking, competitive bulk price.

FAQ

Q1: What is DIN69872-1988 pull stud?

A: DIN69872-1988 is German standard retention knob (pull stud) for DIN69871 SK tool holders (SK30/SK40/SK50). Widely used on European CNC machining centers. The spindle drawbar gripper clamps the tapered head of pull stud to lock the taper shank. Two types available: Type A (with central coolant through-hole), Type B (solid, with sealing ring groove).

Q2: What is the difference between Type A and Type B DIN69872 pull stud?

A: Type A: Central through-hole for internal coolant supply, used for through-coolant cutting. Type B: Solid without hole, with O-ring groove to prevent coolant leakage between threads, for non-through-coolant applications. Both share the same 75° clamping taper angle, only differ in coolant structure.

Q3: Can DIN69872 pull stud replace BT (MAS403) pull stud?

A: Not interchangeable directly. DIN69872 has different taper angle, head diameter and groove geometry. Improper mixing causes abnormal load on gripper, tool change failure, stud fracture or tool drop, which may damage spindle.

Q4: What material and hardness for DIN69872 pull stud?

A: Main material: 20CrMnTi, carburized quenched. Working surface hardness HRC54~57; thread area softened to HRC30~40 to protect tool holder thread. Premium grade adopts 42CrMo for high speed & heavy cutting.

Q5: What is the tightening torque for DIN69872 pull stud?

A: SK30:25–35N·m; SK40:40–60N·m; SK50:80–120N·m. Torque wrench is mandatory. Over-torque damages tool holder thread; insufficient torque leads to loose tool and risk of dropping.

Q6: When should pull stud be replaced?

A: Replace immediately if: indentation, pitting, wear or chipping on 75° taper head; damaged threads or cracks; unstable spindle pulling force and tool wobble. Visual inspection recommended every 500–1000 tool changes.

Q7: Why does coolant leak when using DIN69872-A through-coolant pull stud?

A: 1. Aged or damaged O-ring; 2. Chips/debris in sealing groove; 3. Insufficient tightening torque causing gaps; 4. Damaged threads on stud or holder. Solution: Replace O-ring, clean groove and fasten with standard torque.

Q8: What machining problems are caused by worn pull stud?

A: Worn stud leads to incomplete tool holder clamping, increased radial runout, unstable workpiece dimension & roundness, vibration at high speed, tool jamming or dropping during ATC, and permanent damage to spindle gripper.

Q9: Is old DIN69872-1988 compatible with new ISO7388 pull stud?

A: DIN69872-1988 is old German standard, replaced by ISO7388. Dimensions are nearly identical and compatible in most cases. Confirm spindle gripper structure before purchase; some vintage European machines only accept original DIN69872.