How silly this all looks
It doesn't look like the guy went to the trouble of using steel pipe nipples. This might have been to save money on postage, none of the pictures I saw had more than 6 stamps on the packages, meaning that they probably weighed less than 6 ounces. A 6” x 3/4” pipe nipple with the end caps weighs over twice that much even without powder and a detonating device. So they probably were made with plastic pipe nipples and caps, electrical tape, salvaged wire, and dollar store timers or watches. My guess is that each of the hoax devices cost less than $5 to produce including the postage.