I can feel 'Alex's Socket Set Guide' coming on
There are four socket-set square drive sizes:
- 3/4 inch - bloody massive. Usually used with sockets hub-nut size and up. Few people own these sets - hundreds of pounds to buy. Not really required for work on an Uno, or any car for that matter - you can get 30mm and even 36mm, 41mm sockets in 1/2 inch drive as 'one-offs' when you need them.
- 1/2 inch - large. Necessary for 17mm/19mm sockets, and impact drive sockets (which are usually matt black). I notice that later Unos have a few odd sizes (such as 16mm) cropping up in the suspension - again, those need 1/2" drive for best effect. Everyone should have a 1/2" 'breaker bar' - a swivelling head with solid bar about 750mm long, over which you can place a piece of tubing to get more leverage (never do this to a ratchet handle!) Dunno why a breaker bar is seldom included in a socket set.
- 3/8 inch - medium. Ideal size for 13mm and (in my experience) spark plug sockets. 3/8" socket sets often include a great range of socket sizes (most of which you'll never use) but horrid coarse ratchet handles abound. So two worthwhile additions are a long extension (about 3x longer than the set-included extension), and a quality ratchet handle (I use Snap-on). I never use a universal joint (even though I have one) - 3/8" would be the size in which to get one of those if you're keen.
- 1/4 inch - small. Ideal for 10mm deep socket (probably the 2nd-most frequently-used tool in my toolbox after the Philips screwdriver). 8mm is also common, 7mm and 6mm exist on FIATs (mainly on electrical fittings e.g. the alternator). Again it is sometimes useful to have an extension for 1/4" size.
Try to avoid those 3/8-1/4" 'reducers' at all cost. Nothing but grief ensues (the 1/4" square just shears off). Most sets include a reducer and a screwdriver handle instead of a 1/4" ratchet. Get a 1/4" ratchet when you can
Chas I think you were referring to 3/8" drive - I would be very surprised if you had a 1/8" socket drive, as that would be TINY (less than 4mm!)
Inches never come naturally to me (oh no, what have I just said...) and I always have to think really hard about fractions like 5/16", 17/32", etc. Millimetres are so much easier...
-Alex