Is that a weber brush?
IMO the most common things to cause brush bristles too break off is either
A. It's a cheap brush.
B. The user it's too rough with the brush , pushing down on it too hard, or trying to clean between the spokes.
C. Never cleaning the muck and carbon out of the brush.
The Weber 6493 brush is the best one on the Market. I've been using mine since either 2012 or 13 , and while there's been plenty of bellyaching around here since then, I am very confident it's never had a problem with breaking apart.
In my opinion having a bristle break off, become dislodged, or get swallowed and injure somebody is extremely rare.
I use this Weber 6493 brush and have NEVER had a problem with it. Sturdy, well made, does the job extremely well.
