A polyurethane bush with a 54mm outside diameter, sized to sit inside a mounting bracket or clamp of matching bore. Polyurethane is the right material for this job because it is firm enough to hold a component solidly in place yet compliant enough to absorb the constant high-frequency vibration that a fuel pump produces. That vibration is what cracks brackets and loosens hardware over time, and a rubber-type isolator is what stops it reaching the chassis. The 54mm size is the smaller of the two we list, so match it against your bracket bore rather than the diameter of the pump body. Polyurethane also resists fuel and oil contact far better than natural rubber.