I bought this heater guard around a year ago because my turtle kept breaking her heaters- she entertains herself by knocking the heater into the glass of her tank over and over again.I'm currently using an eheim 250 watt heater and this guard fits it perfectly. I remember it was a bit tricky to get it on the heater though because of the very snug fit, but it *will* fit if you patiently wiggle it on for several minutes.So far, so good. The heater hasn't succumbed to my turtle's assaults and I've had no problems with this guard. Will update if or when the heater guard breaks down.