The valvecap works fine, and it's a perfect fit, however, while it solved one problem another cropped up, making it a semi-worthless buy. If they sold this with the float, it'd be pefect, as you need the float to form a perfect seal against the top pin hole on top of this valvecap to stop the flow of water when the tank is full. On the underside of my float arm, the rubber had taken a set to the previous valve cap, and this nipple didn't sit in the precise old spot, so of course it didn't stop filling the tank when the float "floated".
So I had to buy the whole assembly, of which I only took the new float out of it, and placed it on top of this valvecap and everything else that was still in the tank.
Spend the $10 and get the whole assembly, and you'll have both the float and the valvecap. You'll probably need both.