Low Castle Nut
Our DIN 937 low castle nuts are reduced-height castellated nuts with slots cut into the crown to accept a split (cotter) pin. The pin passes through the slots and a cross-drilled hole in the bolt or axle, positively locking the nut against rotation — the trusted mechanical lock for wheel axles, clevis pins, and steering linkages where space is limited.
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Low Castle Nut — Metric Sizes
What Is a Low Castle Nut?
A low castle nut — also called a low slotted nut or thin castellated nut — is a hexagon nut with a reduced overall height and a castellated crown featuring radial slots. After the nut is tightened on a cross-drilled bolt or axle, a split pin (cotter pin) is inserted through two opposing slots and the hole in the bolt, then bent over to create a positive mechanical lock that cannot vibrate loose. Manufactured to DIN 937, low castle nuts provide the same fail-safe locking as standard DIN 935 castle nuts in a shorter, lighter package, which suits wheel spindles, clevis joints, steering and suspension linkages, and agricultural pivot pins where axial space is tight.
Key Features and Benefits
- Positive Split Pin Locking: The split pin passes through the crown slots and bolt hole, mechanically preventing rotation — a fail-safe lock independent of friction or torque.
- Low-Profile Design: Reduced nut height (DIN 937) saves axial space and weight compared with standard castle nuts, ideal for compact spindle and clevis assemblies.
- Adjustable Locking Position: Multiple slots let you fine-align the pin hole without over- or under-torquing — essential for setting bearing play on axles.
- Visual Inspection: The installed split pin is visible at a glance, simplifying safety inspections on vehicles and machinery.
- Reusable Nut Body: The nut itself is fully reusable; only the inexpensive split pin is replaced at each service.
Materials and Finishes
- Carbon Steel (Plain or Zinc Plated): Standard material for automotive, agricultural, and general machinery pivots.
- Carbon Steel Class 8: Higher-strength option for loaded axle and suspension joints.
- Stainless Steel (A2 / A4): For marine steering linkages, food machinery, and corrosive outdoor environments.
Standards Compliance
- DIN 937 — Hexagon slotted nuts and castle nuts, low (thin) type
- DIN 935 / ISO 7038 — Reference standards for hexagon slotted and castle nuts
- DIN 94 — Split (cotter) pins used for locking
Size Range and Availability
Available in M8 through M52 in metric coarse and fine thread.
Frequently Asked Questions (FAQs)
1. What is a low castle nut used for?
Low castle nuts lock components on cross-drilled bolts, axles, and clevis pins — typically wheel spindles, tie rod ends, steering and suspension linkages, trailer couplings, and agricultural pivot joints — wherever a positive mechanical lock in limited space is required.
2. What is the difference between a low castle nut and a standard castle nut?
A low castle nut (DIN 937) has reduced overall height compared with a standard castle nut (DIN 935). The locking function is identical; the low version saves axial space and weight in compact assemblies.
3. How do you install a low castle nut?
Tighten the nut to the specified torque, then rotate it slightly (normally tighter) until a pair of slots aligns with the hole in the bolt. Insert a new split pin through the slots and hole, and bend the legs over to secure it.
4. What size split pin fits a low castle nut?
The pin diameter must match the cross-hole in the bolt, which is sized per standard for each thread. For example, M12 castle nut assemblies typically use a 3.2mm DIN 94 split pin — always confirm against the bolt drilling.
5. Can low castle nuts come loose under vibration?
No — once the split pin is installed, the nut is mechanically prevented from rotating regardless of vibration. This is why castle nuts remain the specified lock for safety-critical axle and steering joints.
6. Should you loosen or tighten a castle nut to align the slots?
Standard practice is to tighten slightly past the specified torque to the next slot alignment, never loosen, unless the assembly instructions (for example, bearing pre-load settings) state otherwise.
7. Are low castle nuts reusable?
Yes, the nut body is fully reusable. Only the split pin must be replaced with a new one each time the joint is disassembled.
8. What is the DIN standard for low castle nuts?
Low castle nuts are manufactured to DIN 937, which specifies the reduced-height slotted and castellated nut dimensions; DIN 935 covers the standard-height equivalent.
9. What sizes do you stock for low castle nuts?
We stock M8 through M52 in both metric coarse and metric fine thread, in plated carbon steel and A2/A4 stainless steel.
10. Do low castle nuts work for setting wheel bearing pre-load?
Yes. The slot-by-slot adjustment lets you set bearing play precisely and then lock the position with the split pin, which is why low castle nuts are standard on trailer and vehicle wheel spindles.
