Custom Castle & Slotted Nuts

Need a castle or slotted nut a stockist can't supply? If it's a non-standard size, an odd or vintage thread, an exotic material, or a nut defined only by your drawing or an old sample, we machine it to order — standard DIN 935 sizes too, from a single piece.

What Is a Castle Nut?

A castle nut is a hexagon nut with a turned-down cylindrical crown above the hex, cut with slots (the "castellations" or turret) across the top. A split pin, cotter pin, taper pin or locking wire passes through the slots and a cross-drilled hole in the bolt or axle, mechanically preventing the nut from turning. It's the fastener you reach for where vibration would loosen an ordinary nut, but the joint must not be over-torqued — the pin, not friction, holds it in place.

Castle nut vs slotted nut — the difference

The two terms are often used together but aren't identical. A castle (castellated) nut — DIN 935, BS 1768 — has the raised crown, so the slots sit clear of the bearing face; it's the taller, classic "castle" shape. A plain slotted nut — DIN 979 — is thinner, with the slots cut straight into the hexagon and no crown. Both take a locking pin; you choose by height clearance and the standard your assembly calls out. We make both, plus the round slotted nuts (DIN 1804) tightened with a hook or C-spanner.

Types We Machine

DIN 935 Castle Nut Dimensions

Standard metric DIN 935 (coarse pitch) reference dimensions. We machine these off the shelf, and any non-standard size, fine pitch or imperial thread to the same quality:

Thread	Pitch (mm)	Width A/F, s (mm)	Total height, m (mm)
M4	0.7	7	5.0
M5	0.8	8	6.0
M6	1.0	10	7.5
M8	1.25	13	9.5
M10	1.5	16	12
M12	1.75	18	15
M14	2.0	21	17
M16	2.0	24	19
M20	2.5	30	22
M24	3.0	36	27
M30	3.5	46	33
M36	4.0	55	38

Width across flats follows current DIN 935 / ISO 7035. Older DIN 935 and many vintage nuts use a larger across-flats (e.g. M10 = 17 mm, M12 = 19 mm, M22 = 32 mm) to match standard hex nuts — we machine those and imperial (UNF/UNC, BSW/BSF) sizes too. Slot width and count are to standard unless you specify otherwise.

Standards We Work To

We manufacture slotted and castle nuts to the recognised standards — or exactly to your drawing:

Family	Standards
Metric castle / slotted	DIN 935 (castle), DIN 937 (low castle), DIN 979 (thin slotted), DIN 1804 (round slotted), ISO 7035 / ISO 7038
British	BS 1768, BS 3692, and vintage BSW / BSF castellated forms
Imperial / American	ANSI/ASME B18.2.2, UNF / UNC slotted & castle
To drawing	Any non-standard across-flats, crown height, slot count, thread or material

Materials & Finishes

Material	Best for
Steel, class 8 / 10	General and load-bearing castellated nuts; zinc or black oxide
Stainless A2 / A4 / 17-4PH	Marine, outdoor, corrosion-prone joints (A4/316 for saltwater)
Duplex & super duplex	Chloride/seawater with high strength
Inconel / Monel	High temperature and aggressive chemical service
Titanium	Motorsport and aerospace, weight-critical
Brass & bronze	Electrical, decorative and non-sparking

Material certification to EN 10204 3.1 and dimensional inspection are available on request under our ISO 9001:2015 system.

Why Use a Castle Nut?

• Positive locking — a pin through the slot mechanically prevents rotation, not just friction.
• Vibration resistance — stays put on axles, hubs and machinery that would shake a plain nut loose.
• Controlled preload — ideal where the nut must be set to a bearing clearance, not torqued hard.
• Inspectable — the pin is visible, so security can be checked at a glance.
• Reusable — replace the split pin and the nut serves again.

Typical Applications

Castle and slotted nuts appear wherever a pinned, vibration-proof, clearance-set joint is needed:

• Wheel bearings, hubs, stub axles and steering knuckles on vehicles and trailers
• Castor forks, kingpins, tie-rod ends and ball joints
• Machine tool spindles and bearing retainers (round DIN 1804 nuts)
• Agricultural, plant and heavy-engineering pivots
• Classic car, motorcycle and machinery restoration, where the original vintage nut is obsolete

Custom & Non-Standard Castle Nuts — Our Speciality

Stockists carry common DIN 935 sizes in steel and stainless. Everything past that is us: oversize across-flats, custom crown height, extra or narrower slots, left-hand and fine-pitch threads, imperial and vintage BSW/BSF, and exotic alloys. Draw it, or send the nut you're copying — with no tooling cost, one piece is a normal order, and we keep the CAD on file so reorders are quick. See also our special fasteners and custom nuts.

Frequently Asked Questions