1/8" Male thread x 1/4" sae hose fitting with plastic cap.  These are sold as each

Febco 1/4" MIP x 1/4" female thread test cock, low lead. Ordering # 781075LL

Typically used on 1 1/4", 1 1/2" and 2" assemblies.

Fabco 1/8" Male thread x 1/4" Female thread.  Can be used generally on all 1" and smaller backflow line size. Ordering # 781074LL

Part # 18-860XL 1/8" x 1/4" lead free test cock.  This fits assemblies that are 1" or smaller in line size.

1/4" MIP X 1/4" SAE test adapter with plastic cap.   This is referred to as a "fast test cock" because the adapter is already built in.  This fits the 1 1/4", 1 1/2", and 2" sizes

This is only one test cock.  They do sell these in four packs, RK14-860XLFT