Originally Posted by
xenologer
7 and 8 spd cassetes have identical cog spacing, so you can also use shimano 8spd shifters.
Suntour 6 speed shifters can often be modified to index shimano 7, and are very cheap.
The spacing is not identical - it is close, but not identical. 8 speed shifters can often work adequately with a 7 speed cassette but not always. I had a bike for a while that had 7 speed indexed shifters on an 8 speed cassette (certain older shifters allow this) and it never worked to my satisfaction. Friction shifting always works.