In Hollow wall anchor pack (Home Depot # 802454) there are different types of fasteners. Either of the 2 types made of metal fasteners in that kit will work. Tighten them until they are snug, don't over-tighten. Watch the short video HD has next to those fasteners on the website. Those plastic ones in the kit are probably the same type as will come with the Grohe towel bar....... they're almost useless for holding anything with a little bit of weight on it.