The SRAM PC-850 chain works like a champ on an Suntour Ultra 6 or 7 Speed freewheel.
Silly, a Shimano Megarange 6 speed, however is not "Ultra" spaced, and in most cases will not work, because it is sized for 126mm dropout spacing.
But there are work-arounds to this challenge. Tell us more about the bike, post some pictures of the current freewheel and wheel, mounted in the dropouts, and measure your spacing. Tell us a little more about your objectives for the bike's future. What type of freewheel does it currently run.
These are all important pieces of information which help us give some great advice.
Best of luck!
__________________
Bob
Enjoying the GA coast all year long!
Thanks for visiting my website:
www.freewheelspa.com