The length of the cross bars can wary, but not very much.
I have one katar where the cross bars are 6 cm, one where they are 8 cm, but the rest are 7 to 7.5 cm.
Should I use a katar the cross bars would have to be 10 cm.
Have a look at this thread.
http://www.vikingsword.com/vb/showth...bone+structure