The pump stops on a Saturday afternoon. The fault is a loose flange, four bolts, twenty minutes of work. The 13 mm spanner is not in the box, because it is the one that gets borrowed, so somebody reaches for a shifting spanner. It slips twice, the corners of the first nut go round, and now a twenty minute job needs a hacksaw and a trip to town on Monday.
Most farms own spanners. Fewer own the right ones. A set bought on price alone tends to be missing the sizes the machines actually use, made of steel soft enough to spread, and cut loose enough to bear on the corners of the nut instead of the flats. Every one of those faults shows up as a rounded fastener at the worst possible moment.
This is a guide to the sizes that do the real work on tractors, pumps, motorbikes and mills, ring against open against combination, which drive size to buy first, when a torque wrench earns its place, and how to tell a set that will last from one that will round your nuts inside a season.
The Sizes That Do Ninety Percent of the Work
A metric spanner size is the distance across the flats of the nut it fits. Those flat sizes are tied to bolt thread diameters by the ISO standard for hexagon fasteners, which is why the same handful keeps turning up on machines from different countries. An M8 bolt carries a 13 mm head, M10 carries 17 mm (16 mm on some newer fasteners), M12 carries 19 mm, M16 carries 24 mm and M20 carries 30 mm.
On a small engine, a pump, a motorbike or a chaff cutter, the working sizes are 8, 10, 12, 13, 14, 17 and 19 mm. Those seven handle engine covers, fuel line clamps, motor mounts, belt tensioners and most guards. Add 6 and 7 mm for hose clips and small electrics.
The bigger machinery pushes upward. Tractor wheel nuts, implement pins, linkage hardware, pump flanges and the bearing housings and pulley bolts on a posho mill live in the 22 to 32 mm range, with 22, 24, 27, 30 and 32 the ones you meet most often. A set that stops at 19 mm is a motorbike set. A farm needs the second half as well.
One caution on tractors. Many older British and American designed tractors still running in Kenya carry imperial fasteners, and some carry a mix after decades of repairs. A 1/2 inch AF nut measures 12.7 mm, so a 13 mm spanner sits on it with a third of a millimetre of slop, which is exactly how corners get rounded. If your tractor is one of these, a few imperial spanners in its specific sizes beat a bigger metric set.
Ring, Open and Combination: Where the Load Goes
An open ended spanner touches the nut on two flats, one on each jaw. All the turning force goes through those two small areas, and as the jaws take load they spring apart slightly. Under a hard pull the contact walks toward the corners of the nut, and the corners are what fail. Open ends are for speed and access: reaching a nut from the side, running a nut down a long thread, holding a bolt head while the other end is tightened.
A ring spanner closes around the nut and shares the load across all six corners or, on a flank drive pattern, across the flats just inboard of them. It cannot spread and it cannot slip off sideways. The final tightening and the first crack loose belong to the ring end every time.
A combination spanner puts a ring on one end and an open jaw on the other, both the same size. For a farm this is the right pattern for the main set, because one tool does both jobs. Double ended spanners, ring on both ends or open on both, put two adjacent sizes on one tool and are cheaper per size, so they make a good second set for the truck or the pump house. Double open end spanners appear on our price list at 1,600 KSH (code HKSPA2088).
Two specialised patterns are worth knowing. A flare nut spanner is a ring with a slot cut in it so it slides over a pipe, and it is the only tool that will undo a hydraulic or diesel injector line fitting without rounding it. A shifting spanner is the tool everybody owns and nobody should use on anything they care about: its jaws are never parallel under load and it rounds nuts faster than anything else in the box. Keep one for holding, not for turning.
1/2 Inch or 3/8 Inch Drive
Socket drive size is the square peg on the ratchet, always quoted in inches even on a metric set. It sets how much torque the tool can carry and how big a socket can be made to fit it. The two that matter here are 3/8 and 1/2 inch.
A 3/8 inch drive set typically covers 8 to 19 mm. The ratchet head is small, the sockets are slim, and it gets into the places on an engine or motorbike where a 1/2 inch ratchet will not fit. Its limit is torque: put a long bar on a 3/8 inch ratchet to shift a seized 19 mm bolt and you will strip the ratchet gear or twist the drive square.
A 1/2 inch drive set covers 10 to 32 mm and is the one you put a breaker bar on. Tractor wheel nuts, mill pulley bolts, pump flange bolts, motorbike axle nuts and anything rusted in place all belong to 1/2 inch, and it matches the impact guns most workshops run. If the farm has a tractor or a mill and the budget allows one set, buy 1/2 inch first and add 3/8 inch for the small work later. If the work is mainly motorbikes, pumps and small engines, reverse that order.
Within any drive size, the socket itself comes in two patterns. A 6 point socket has six flats and grips the nut on its faces. A 12 point socket has twelve corners and finds the nut in twice as many positions, but it bears on the corners, and on a rusty or slightly undersized nut it will round them. For farm work, 6 point is the default. Deep sockets, roughly twice the length of a standard socket, reach a nut on a long stud: a pump flange, an exhaust manifold, a mill bearing housing.
Torque Wrenches: The Bolt That Is Neither Loose Nor Stretched
A bolt holds because it is stretched. Tightening it to its correct torque stretches it a fraction within its elastic range, and that stretch is the clamping force that keeps the joint tight under vibration. Too little and the joint moves and the bolt works loose. Too much and the bolt yields, loses its spring, and either snaps on the spot or fails a week later.
Tightening by feel gets both wrong. A strong fundi on a long bar overshoots the torque for an M8 bolt several times over, which is why cover bolts on small engines so often shear on the second service. The same fundi undershoots the big fasteners, because a 30 mm wheel nut needs more torque than an arm can deliver on a short ratchet.
A click type torque wrench solves this. You set the value, pull steadily, and the wrench clicks when it gets there. A 1/2 inch drive wrench covering roughly 40 to 200 newton metres suits wheel nuts, cylinder heads, pump flanges, mill hammers and bearing housings. A 3/8 inch wrench in the 10 to 60 newton metre range covers engine covers, sump plugs and motorbike work. The figures come from the machine's manual, or from a general table for the bolt size and the grade stamped on its head.
Using it correctly matters more than owning it. Pull smoothly and stop at the click; a second pull overtightens. Never use it to loosen a nut or as a breaker bar, because both damage the mechanism. Tighten in a star pattern on a wheel or flange so the clamping load comes on evenly. When you are done, wind the wrench back to its lowest setting so the spring relaxes, and keep it in its case.
How to Spot a Set That Will Round Off Nuts
The steel comes first. Good spanners and sockets are forged from chrome vanadium steel, marked Cr-V on the tool, and heat treated so they are hard enough not to spread but not so brittle that they crack. A tool that says nothing about its steel is usually carbon steel of unknown treatment. Its jaws open a little more with every hard pull until one day a 13 mm spanner is a 13.5 mm spanner that fits nothing properly.
Fit comes second and you can test it in the shop. Put a socket on a nut of the same size and rock it. A good socket has a small, even clearance and almost no rotational play. A loose one rocks visibly, and every degree of play is a degree of rotation before the socket touches the nut, which means it hits the corners rather than settling on the flats.
Look at the markings. Sizes stamped or etched into the metal stay readable for the life of the tool; sizes painted on wear off in a month. Look at the chrome as well: thin plating already flaking at the edges of the socket opening will peel into the bolt and rust underneath.
Work the ratchet. Turn it slowly in both directions and feel for clean, even clicks with no skipping. A ratchet with more teeth, 72 rather than 36 for example, needs a smaller swing to pick up the next tooth, which is what lets you work in tight spaces. Then load it gently against a fixed bolt: a mechanism that slips or crunches under moderate hand pressure will fail on the first real job.
Finally, count the set honestly. A box marked as 150 pieces often holds forty sockets, a dozen spanners, and a hundred poor bits and hex keys that pad the number. What matters is whether the sizes you use are present, in the drive size you need, in 6 point, with a deep socket for the ones on studs. The right 40 pieces beat the wrong 150. Our hand tool starter kit guide applies the same thinking to the rest of the toolbox.
A Sensible Starter Set, and What to Add Later
Start with the tools that cover the most fasteners on the most machines, and let the next purchase follow the next machine. This is a starter list for a mixed farm with a pump, a motorbike, a chaff cutter or mill, and occasional tractor work.
Combination spanners, 8, 10, 12, 13, 14, 17, 19, 22 and 24 mm. Nine tools that fit almost everything below tractor size. Buy them on a rail or in a roll so a missing one is obvious.
A 1/2 inch drive socket set with 6 point sockets from 10 to 32 mm, a ratchet, a short and a long extension, a universal joint, and a breaker bar at least 450 mm long. If the set does not include the breaker bar, buy one separately.
Deep sockets in 13, 17 and 19 mm, and a spark plug socket for your engines, commonly 16 or 21 mm.
Hex keys, metric, 3 to 10 mm, because grub screws on pulleys and collars use them and nothing else will do.
That set does the pump, the bike, the mill and most of the tractor. Add later, in roughly this order: a 3/8 inch drive set with 8 to 19 mm sockets for engine and motorbike work in tight spaces; a 1/2 inch click torque wrench once you refit wheels, heads or hammers yourself; a flare nut spanner set if you maintain injector lines or hydraulics; stubby combination spanners for the places a full length handle will not swing; and, if the tractor turns out to be imperial, the specific AF sizes it needs.
Do not add a shifting spanner. You already have one. Do not add a second 150 piece box because it was cheap; add the individual sizes you have found yourself needing. A vernier caliper earns its place beside the socket set, because measuring a nut across the flats before reaching for a spanner is what stops you fitting 13 mm to a 1/2 inch AF nut in the first place.
Everything on this list is stocked across our six branches, with spanner sets, socket sets, torque wrenches and breaker bars in our workshop and industrial tools range. Bring a list of the machines you run and the counter staff can match the sizes to them.
Key Takeaways
- Seven sizes, 8, 10, 12, 13, 14, 17 and 19 mm, cover most small engine, pump and motorbike work. Mills and tractors add 22, 24, 27, 30 and 32 mm.
- Older tractors may carry imperial fasteners. A 13 mm spanner on a 1/2 inch nut has slop, and slop rounds corners.
- Crack loose and final tighten with a ring end or a socket. Use the open end only for running a free nut.
- Buy 1/2 inch drive first for tractor and mill work, 3/8 inch first for motorbikes and small engines. Choose 6 point sockets.
- A click torque wrench keeps bolts stretched but not yielded. Use it only to tighten, and wind it back after use.
- Test a set by rocking a socket on a matching nut, checking for Cr-V marking and stamped sizes, and working the ratchet under gentle load.
- Buy the right 40 pieces, not the wrong 150, and let each machine you add decide the next purchase.
Frequently Asked Questions
Which spanner sizes are used most on a farm in Kenya?
For the engines, pumps, motorbikes and small machines on a typical farm, the sizes that do most of the work are 8, 10, 12, 13, 14, 17 and 19 millimetres. Tractors, mill bearing housings and pump flanges add 22, 24, 27, 30 and 32 millimetres. A set that stops at 19 millimetres will handle a motorbike and a small pump but not a tractor wheel or a posho mill pulley.
Should I buy a 1/2 inch or 3/8 inch drive socket set?
Buy 1/2 inch drive first if the farm has a tractor, a mill or any bolt above 19 millimetres, because it takes a breaker bar and an impact gun without breaking. Buy 3/8 inch first if the work is mostly motorbikes, small engines and pumps, where the sockets are smaller and access is tight. Most workshops eventually own both and use each for the range it suits.
What is the difference between a 6 point and a 12 point socket?
A 6 point socket has six flats and grips the nut on its faces, so it cannot round the corners and is the right choice for rusty, seized or high torque fasteners. A 12 point socket has twelve corners and fits the nut in twice as many positions, which helps in tight access, but it bears on the corners of the nut and will round a soft or corroded one. For farm work, 6 point should be the default.
Do I need a torque wrench on a farm?
If you refit tractor wheels, cylinder heads, pump flanges, mill hammers or bearing housings yourself, yes. A click type 1/2 inch drive torque wrench is enough. Bolts done up by feel are usually either loose enough to work free under vibration or so tight they stretch and snap. Use it only to tighten, never to loosen, and wind it back to its lowest setting after use.
How can I tell if a cheap socket set will round off nuts?
Fit a socket to a nut of the same size and rock it. Noticeable play means the socket bears on the corners and will round them. Look for chrome vanadium steel marked on the tool, sizes stamped rather than painted, and a ratchet whose teeth engage cleanly with no skipping. Thin chrome that flakes at the edges, a ratchet that slips under load and a case that will not hold the sockets are all signs of a set that will not last a season.