Both of these are labeled 1". The T on the left fits the little bit of grey pipe. The valve on the right is too small. What am I missing?
That valve is for a different type of piping system called CPVC and the sizes and fittings are different. The difference is deliberate because CPVC is rated for hot water whereas regular PVC is not; they don't want people to accidentally (or deliberately, to save money) install regular PVC pipe or fittings on a hot water system.
Look at the valve label.
When plastic piping systems were first introduce to the market, the manufacturers tried to make them similar to metalic piping systems so "pipers" would accept them. So they adopted similar wall thicknesses to schedule 40 and sch. 80. Piping systems have to be checked against the pressure and temperature of the process fluid. Here in was the problem. Adopting sch. 40 an 80 wall thickness caused inconsistant P-T rates for different sizes of plastic pipe. The solution was to create plastic pipe with a SDR, which stands for Standard Dimensional Ratio. SDR piping has the same P-T ratings regardless of pipe size.
Could one of you pipe and valve components be for a scheduled piping system and the other for a SDR piping systems?