• Ever grab for example a 13mm socket and it's too tight, but 14mm feels loose? And it's not SAE?
• Not every bolt and nut on vehicles remain factory perfect to the millimeter over time and service life
• Use 0.5mm under sockets for rounded and damaged bolts and nuts
• Use 0.5mm over for swollen or corroded bolts and cap covered nuts
• For hand tools and impact wrenches, use a hammer to fit 1/2 size under sockets where needed