I have several 13mm 2-port gyrojets as shown in the photo below.
Previously, I have only see 4-port gyrojets. Is the 2-port version less common than the 4-port? Did the 2-port precede the 4-port version?
Can a gyrojet be sent through the US Post Office or does it need to go Parcel Post?
Any help and information would be greatly appreciated.