Because of the way the head and spring bars are designed the bars will only fit the head of the same rating. I know most systems will let you swap out the bars, and that would certainly be ideal. If you want to switch to the 6k bars # EQ90-01-0699 then you will need to replace the head with the # EQ90-02-0600 as well. The brackets and the shank will work for all systems so there is no need to replace those. view full answer...