Odd vs. Even

[Kneescrubber]

While wrenching on both the Beemer and Honda this weekend I noticed that other than the veritable 10mm most bolts on the BMW are odd sized and most on the Honda are even. Curious.  

[garry]

My KTM has lots of 8mm, some 10s, and a few 13s, plus they are fond of both 5mm and 6mm allens as well as three (I think) Torx bits. Many of the hex head bolts also have Torx centers.

[black hills]

my Adventure has a mix of odd and even. and the torx as mentioned. I do like the fact that the torx is also a hex head so you can use a regular socket if you choose. Chain tensioning on the KTM requires a 10 & 13mm while the honda takes 2-12's?

[JSharp]

JIS - Japanese Industrial Standard vs. ISO/ANSI/DIN. Same bolt sizes and thread pitch but different head sizes.

Here's a table that illustrates this - http://www.boltdepot.com/fastener-information/Bolts/Metric-Bolt-Head-Size.aspx

[mxvet57]

What i don't like is when i go to the hardware store for a replacement bolt it's allways an odd size. (11,13,15 mm)