What Is a Hook Wrench? Types and Selection Criteria
A hook wrench is a special wrench that tightens and loosens notched round nuts by engaging the lug at the end of its arc-shaped body in a notch.
A hook wrench is a special wrench that turns round nuts with notches cut around their circumference by engaging the lug at the end of its arc-shaped body in a notch. It is used to tighten and loosen notched bearing nuts that secure bearings to shafts, adjusting nuts on machine shafts and similar notched rings that have no hex faces.
Types of hook wrenches
| Type | Tip | Nut it fits |
|---|---|---|
| Square-end hook wrench | Square lug at the end of the arc | Nut with square notches around its circumference |
| Pin-type hook wrench | Round pin at the end of the arc | Nut with round holes around its circumference |
| Adjustable (hinged) hook wrench | Hinged arc, wide diameter range | Notched nuts of different diameters |
A square-end wrench does not hold in a nut with holes, and a pin-type wrench does not hold in a notched nut; one cannot replace the other.
Selection criteria
- Nut outer diameter: The two numbers in the size give the nut outer diameter range the wrench fits, in millimetres; a 40/42 wrench fits a nut with an outer diameter of 40–42 mm. Measure the nut with a caliper and choose the wrench whose range covers it.
- Lug and notch fit: The lug must seat fully and squarely in the notch, and the arc must rest against the circumference of the nut. If the notch is narrower than the lug, the wrench will not seat; if it is much wider, the lug works with play and crushes the notch edge.
- Access: The catalogue data gives lengths from 136 mm to 242 mm; when working in a tight space on a shaft, check that there is room for the arc and the handle.
- Material: The wrenches in the catalogue are made of chrome vanadium steel and chrome plated; the manufacturer states the DIN 1810 standard for this product.
Common mistakes
- Driving the notch with a hammer and chisel: The notch edge is crushed, the wrench will not hold at the next removal, and chips can get into the bearing.
- Using the next size up: The arc does not wrap around the nut, the lug is loaded at a single point and slips.
- Fitting it the wrong way round: A hook wrench holds in one direction only; to turn the other way, flip the wrench over and fit it again.
- Extending the handle with a pipe: The lug can break or the notch can be crushed.
- Forgetting the lock washer: On bearing nuts with a tab lock washer, bend the washer tab out of the notch before loosening and bend it back into a notch after tightening.
Hook wrenches in the Welibaba catalogue
The Hook Wrenches category has 7 sizes of the İzeltaş square-end hook wrench, sold per piece: 30/32, 34/36, 40/42, 45/50, 52/55, 58/62 and 68/75. There are gaps between these sizes; for example, none of them fits a nut with an outer diameter of 38 mm or 44 mm.
Wrenches with an adjustable jaw opening are in Adjustable Wrenches, and wrenches that grip pipes and round bodies in Pipe Wrenches.
Frequently asked questions
What does the size 30/32 on a hook wrench mean?
It is the nut outer diameter range the wrench fits: a 30/32 wrench is for notched nuts with an outer diameter between 30 mm and 32 mm.
Can a square-end hook wrench be used on a nut with holes?
No. Nuts with round holes instead of notches around the circumference need a pin-type hook wrench; a square lug does not seat in a hole and slips.
What should I do if the nut diameter falls between two sizes?
Do not force the larger size; because the arc does not wrap around the nut, the lug slips and crushes the notch. Use a size whose range covers the diameter, or an adjustable hook wrench with a wide range.