A hand air pump includes a connecting member having a barrel and an outlet port and a mouth, a receptacle having a cylinder engaged onto the barrel and having a slidable piston, the receptacle includes a channel for engaging with a cover plate which includes a longitudinal hole communicative with the mouth of the connecting member, and a gauge device includes a notch for receiving the receptacle and includes one or more latching members for retaining the gauge device to the receptacle and includes a connector engaged with the hole of the cover plate for receiving the pressurized air from the cylinder and for measuring an air pressure within the cylinder.