Rimba Bondage Play Urethral plug hollow with ring The plug is hollow inside which allows moisture to come out. The penis plug has an increasing diameter of 5 mm to 1 cm and can be inserted for more than 8.5 cm. The ring on the top makes it easy to remove the plug. This bondage accessory can be used with any kind of lubricant and is best cleaned under the tap with a mild soap and then dry and polish with a clean cloth.