Info I found from "way back" says there are four different spring & retainer combinations, so the purchaser needs to determine which spring option fits their application:
TFS-61617801-C00 1.460″ dual valve springs
TFS-61617802-C00 1.550″ dual valve springs
TFS-6161T783-C00 1.550″ dual valve springs w/ ti retainers
TFS-6161T784-C00 1.560″ dual valve springs w/ ti retainers

I know the 1.560" is intended for a solid roller up to .700" lift, but don't know what the others are spec'd for.