Massive thread dredge here but since this is the first Google result for this and there's not really a clear answer on the thread, thought I'd post my experience for the benefit of future kierin grip installers.
NJS kierin grips are designed for 25.6mm clamp bars, which are narrower than usual. Putting them on those, you may be able to get them on with WD40 (RE WD40 and hairspray: they both do exactly the same thing except WD40 dries quicker - usually done in an hour or two, hairspray can take a day or so).
If you're putting them on 31.8mm clamp bars (I was putting them on a set of Deda Velocitas) they are an absolute git and WD40 is not enough. I did the first with it (as that's what I've been using for 15 years) and it took me over an hour, most of the skin off my hand and all the swear words I know. The second I soaked in hot soapy water. Boom. Done in 30s.