The click of a ratchet wrench is the defining sound of a mechanic. Ratchets and sockets are extremely useful and versatile tools for the garage - in this article we explain how a ratchet works and what to look for when choosing one. A ratchet spanner is used to tighten and loosen nuts and bolts. The ratchet mechanism lets it exert undo the nut only in one direction - meaning that you can quickly undo or tighten nuts without having to constantly lift the ratchet off,
as you would with a traditional spanner.Drive sizes
All ratchets accept sockets using a square drive and mostly there are three sizes of drive. Everywhere in the world these sizes are given in inches - even when the sockets are metric.
- 1/4 inch - Used for smaller sockets and precision work. Useful for dismantling individual components on the bench.
- 3/8 inch - The middle sized, and in my opinion, most useful size for general use on a car. A 3/8" drive can drive sockets of all sizes. It is big enough to apply quite a lot of force, but not too big to fit into tight spaces
- 1/2 inch - 1/2" sockets are generally used for nuts and bolts from around 10mm and up. A 1/2" drive socket can apply enough force to undo all nuts on a car.
- There are also 3/4" and 1" ratchets but these are used on trucks, tanks and industrial machinery.
Tooth count
Inside a ratchet there is a toothed wheel which lets it freely rotate as you tighten the nut. Each click you hear is a tooth passing the ratchet. The more teeth there are, the less movement is needed on the return stroke. A ratchet with 75 teeth will work considerably faster than a 32-tooth ratchet. Making high tooth-counts requires quality engineering and manufacturing, so as a general guide the better quality tools will have a higher tooth count.
Socket release
Sockets are held onto the ratchet using a little spring-loaded ball on the side of the square drive. After applying a lot of force, I've often found sockets get stuck on the drive and the only way to get them off is to hammer the ratchet on the floor or even grip it in a vice. Good quality ratchets include a button on the back which smoothly pushes off the socket when you are ready to release it.
Choosing yours
More than any other tool, a ratchet will last you a lifetime. Quality ratchets can be serviced inexpensively and so should never wear out. Sockets are interchangeable because they are all standard. Buy the best ratchet you can afford, even if you buy inexpensive sockets to start with. My go-to ratchet was made in the 1960s and inherited from a family friend. I still use it every day.
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There is a correct answer. I'm not 100% sure I know it, but here goes my attempt:
Each fastener size has a recommended torque rating based on it's:
1) usage
2) size and thread pitch
3) grade
In normal use, you should see most fastener torques somewhere near their target. For example, your 1/2" socket fits a 5/16" diam bolt. Roughly speaking, a Grade 5 5/16-18 should be torqued somewhere around 20ftlbs. I would recommend a drive system with roughly twice that capability, since corrosion, frictions etc all may conspire to cause you to apply more than the recommended torque to loosen.
For Snap on Dual 80 ratchets (as I recall), the max recommended torque for 1/4" is around 90ftlbs, for 3/8 it's 250ftlbs, for 1/2 its 750ftlbs. By giving your self a 50% margin, your 1/4" drive can be safely used for fastsners upt to 3/8" dia which require 9/16" sockets (the largest Snap On makes).
In metric, head sizes differ for a given thread. M10 should really be the limit. That would be a 14mm socket under the Japanese std, and a 17mm socket under the German std. I don't believe Snap on Makes a 17mm 1/4" drive socket. Under the Japanese Std (JIS) M12 bolts have 17mm heads (and require 70ftlbs).
3/8" drive ratchets are good for 250ftlbs, allowing use on fastener at least up to 9/16 dia. (13/16" heads) or M14 (22mm head for German std).
What I think you will notice is, socket manufacturers tend to make sockets in drive sizes that allow their use for the attending bolt diameters. If you stick to the std set sizes, 5-15mm in 1/4" drive, 8-21mm in 3/8", you should be okay.
Personally, I use the smallest drive I can for any application. My recommendtaion is:
1) use std length handles, which limit your ability to comfortably apply more torque than the drive can take. If you feel you need a longer ratchet, choose a larger drive.
2) never use an adapter
3) don't buy specialty sockets for small drives
(32mm 3/8" drive for example)