This design in openscad is for an antenna insulator used when building hamradio antennas or could also be used for electric fences. The standard design is about 40mm long with 8mm holes for rope and or wire, but can be scaled as needed or the source code can be changed.
A unique 2 piece version has been designed for applications that need an insulator added in the middle of a wire (think loop antennas). The 2 piece insulator is assembled using 3mm stainless cap screws.