A great accessory to diversify your strap-on arsenal. It is great for that special two-way penetration, exciting both to the harness wearer and his/her partner. This double dong can also be used without any harness at all. Double Dong Plug Box. Double Dong Plug is an attachment for the Vac-U-Lock Modular System. Can have two Vac-U-Lock dongs attached to be used as a double dong without a harness. Made using phthalate free, non-toxic materials ABS plastic. ABS is hard plastic, non-porous, durable and easy to clean and maintain. All types of lubricants may be used with hard plastics but be sure to clean well around seals. ABS products are safe, pure plus phthalate free. Vac-U-Lock is a US patented harness attachment system. It was the first of its kind 20 years ago when it was developed and still continues to be the strongest brand name in harness systems today. With countless attachments, plugs and full harness systems, Vac-U-Lock is an all-encompassing modular sex system that gives the user the ability to pair different attachments with different harnesses and Vac-U-Lock plugs to create infinite possibilities. Vac-U-Lock Modular System from Doc Johnson Novelties The Great American Toy Company. New image added May 22, 2013.