Plain nuts come in different heights standard or thin, pitches standard (coarse) or fine, one or two sided bevel, and standard or small head. Sorry but you will have to choose from that many options and of course the material and platting!
Japanese motorcycles usually use fine pitches for M10 and above. So you may need M10 x 1.25 and M12 x 1.25 which are not common in hardware stores and overpriced in bike shops.
Nut Standard - One Bevel
On this page you will find nuts with standard height and width. Comes in two pitch variations standard and fine. Only one bevel at the bottom, common in Japan and old bikes. Sizes in millimeters.
Height Width Pitch M3 2.4 5.5 0.5 M4 3.2 7 0.7 M5 4 8 0.8 M6 5 10 1.0 M8 6.5 13 1.25 M10 8 17 1.5 M12 10 19 1.75
Standard size with fine pitch
Height Width Pitch M8 6.5 13 1.0 M10 8 17 1.25 M12 10 19 1.25