These straight adapter fittings are 1/4-18 NPT (National Pipe Thread) Male, and 1/2" OD Hose-Barb on the other end to fit with 1/2" ID hose or tubing.
These are multi-purpose fittings and may possibly be used for Automotive, Boat (Marine), Hydroponic, Irrigation, Pneumatic, Agriculture, and Aquarium applications.