Slack-R is now compatible with MOST Tapered IS headsets. There are 3 different styles of upper cups now to go along with the IS52 lowers. IS41, IS42, and IS42S.
IS41/IS52 will fit a number of bikes from manufacturers such as Yeti, Santa Cruz, and Trek (eliminates the need for a Knock Block in most cases). Cube is an exception as they use a deeper upper bearing seat and the Slack-R IS41 will not sit properly in the Cube frames.
IS42/IS52 will fit many bikes from Cannondale, Norco, Marin, Orbea, GT, Revel, Scott and many more including some Specialized with a standard depth IS42/IS52 headset. Standard bearing seat depth is 3mm
IS42S/IS52 will fit Specialized bikes that have the 6.8mm deep upper bearing seat. (some Specialized bearings sit deeper than the standard IS42 geometry so they require their own specific top cup to insure proper fitment)
Headset types do vary across the same manufacturer, make sure you are sure what kind of headset you have. (IS/EC/ZS or hybrids of these)
Some IS bearing seats in the frames have a smaller bearing seat inside diameter than others so in some cases a bit of sanding will be required to fit in the 34.5mm upper sleeve and 44.5mm lower sleeve. In most cases the frame allow the kits to drop right in but in some cases opening up the upper and/or lower bearing seat inside diameter(s) will be required so double check your frame clearance prior to ordering if unsure.
Contact firstname.lastname@example.org if you are unsure about your application prior to ordering.