The grips that came on K bikes are hard rubber and they suck.  On all of my K bikes I use Pro/Grip model 699 grips.  They're gel and are much more comfortable.  They work fine with either BMW or aftermarket heated grips.  They come in both closed and open ended styles under the same number so if ordering online then be sure you know what you're ordering.

Hair spray works well for installing grips.  It first acts as a lubricant to let them slide on easily and then sets up to hold them in place.

 

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