Older cars and bikes,made before the 60's often use fixings that need whitworth,BSF or af spanners,some much later specialised vehicles carried on using whitworth for years after others had stopped..Many vehicles made up to the mid 70's use bolts that need af tools and later ones use mainly metric.There are no dates set in stone,but the older the vehicle the more chance your metric tools won't fit the majority of the nuts and bolts that hold it together.So,how do you tell the difference?.

First the easy bit.Metric tools fit metric threaded nuts and bolts.the odd one might fit a whitworth,BSF,BA or UNF nut or bolt but it wasn't designed to.If it says 19mm on the spanner it's made to fit a nut or bolt 19mm across the flats (ie) wide.Thats it simple and really rather boring.

Remember the term "across flats" ?. If you find a spanner marked say 1/2 af,it means the spanner is designed to fit a fastening 1/2 inch wide or across flats (ie) a.f. The spanner might simply be marked 1/2 or 1/2 SAE some are even marked something like .50 SAE (the decimal equivalent of 1/2 inch) for example.The thread of the bolt should be either UNF or UNC but the spanner carries the head sizes stamped on it,all simple easy stuff.The we come to whitworth and BSF.Here the spanner or socket might carry two sizes for example 7/16 inch whitworth / 1/2 inch BSF.This means the tool will fit nuts and bolts with those thread sizes.Sometimes only one standard will be marked on the spanner but a 7/16 whit will always fit a 1/2 bsf all through the range the spanners are will fit both standards always one size apart so you only need one se of spanners to do both!Whitworth incidentally was one of the first attempts at a standard thread and is named after the British engineer who invented it,BSF stands for "British Standard Fine" it is in effect the fine version of Whitworth.Thread guages are the easiest way to identify the different standards,a lot of bolts are marked but it's almose imopossible to list all the markings that have been used by different manufacturers over the years.A spanner or socket should fit snugly on a nut in good clean condition,if it's loose its probably the wrong one.

The other 'imperial' size to confuse things is BA. BA fittings are used on lots of older machinery especially electricl stuff,the common sizes are 4 and 2 BA.The smaller the number the bigger the spanner and they go from 0 to 11BA.All BA fixings have a set thread and head size so a 2BA spanner fits a 2BA socket or bolt.

Complicated? Maybe but all part of the fun of owning a vehicle or machinery made before the days when plastic and planned obsolescence became the norm.Best of luck with it.