The size of the ball float is directly related to the size of the float valve inlet thread. Not forgetting that this thread is measured in BSP (British Standard Pipe). Most plumbing products thread sizes are stated as BSP imperial thread measurements which means that the actual diameter of the thread is approximately 1/4 inch larger than that stated in BSP terms. For example a 1 1/4 inch BSP Float Valve has an actual thread diameter of approximately 1 1/2 inches. If the float valve has an actual diameter of 1 1/4 inches it is in fact a 1 inch BSP thread, therefore a 1 inch float valve. Below you will see a table indicating the float ball required for each size of float valve. Use this link to see our range of float balls and float valves

Float Valve Size (BSP)	Float Valve thread dimensions (actual)	Float Ball Size	Float Ball Thread Size
1/2 Inch BSP	3/4 Inch	4 1/2, 5 or 6 Inch	5/16 Inch
3/4 Inch BSP	1 Inch	4 1/2, 5 or 6 Inch	5/16 Inch
1 Inch BSP	1 1/4 Inch	8 Inch	7/16 Inch
1 1/4 Inch BSP	1 1/2 Inch	10 Inch	9/16 Inch
1 1/2 Inch BSP	1 3/4 Inch	10 Inch	9/16 Inch
2 Inch BSP	2 1/4 Inch	12 inch	5/8 Inch