Product Details:

This injection point check valve has a 1/2" MNPT outlet and is made of polypropylene with Viton elastomers. It includes a 5 lb spring made of hastelloy and goes with Chem-Pro's C2 series diaphragm metering pumps.

See the spare parts diagram in the thumbnails on the left, it's highlighted as #30 on the bottom right of the illustration.