How to find spanner size from bolt diameter ?

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Following formula are used to calculate spanner size –

For bolt size upto M14

Spanner Size = ( Bolt Size * 1.5 ) + 1

Example for M12 bolt , Spanner Size = ( Bolt Size * 1.5 ) + 1 = ( 12 * 1.5 ) + 1 = 18 + 1 = 19

Above from M16 bolt  

Spanner size = Bolt Size * 1.5

Example for M16 bolt , Spanner Size = Bolt size * 1.5 = 16 * 1.5 = 24

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