It's confusing to me, because I always thought motorcycle bars were wider in diameter - now I see tons of clamps that say 7/8 or 22mm which is exactly the measurement I get from several bicycle bars I have...
There are three different standard size handlebars, 3/4", 7/8", and 1". All three sizes are found on motorcycles and atv's, but 7/8 is the standard for most bicycles, and also a common size on motorcycles nowadays.
There are tons of these mount brackets on ebay, just measure your bars to be sure you get the right ones... bicycle bars are typically 7/8" but in some not so common cases I've seen 1" bars on bicycles as well.