What is the difference between metric and harley motorcycle handlebars?

All motorcycle handlebars come in 4 sizes - 7/8", 1", 1.25" and 1.5". This is true for Harley and for Metric bikes. Other than off-road or smaller bikes that use 7/8" bars, most stock bikes run with 1" bars. The real difference between Harley and Metric bars come in the bolt sizes and the riser spacing - both apply to attaching the bars to the upper triple clamp of the bike's front end.

Harleys use a 3.5" centre to centre spacing for the risers and the bolts are 1/2"-13. Metric bikes use a range of options - some use 3.5" centres, others 100MM and still others use 120MM. Bolts can be 1/2"-13 or metric bolts in the M12-1.25 x 40mm size range. Usually a single maker sticks to a common size for riser spacing and for bolts for all their bikes, but at least one company isn't consistent so check to be sure.

Generally, controls are for 1" bar ends so the larger diameter bars step down to 1" for the control and grip sections. However, just because the ends are 1", it doesn't mean that all stock controls and grips will fit. Additionally, some bars have the risers welded on and are bike specific because the angle is designed to allow pull back towards the rider and still ensure they will clear the stock tank and/or instrument console when turned from side to side.