Sam STP Packer by New York Toy Collective can be used without a harness.  It fits in regular underwear or packing underwear.  Just hold it steady, aim, and let it flow!  It is 5.6 inches long, 2 inches wide, and has 3 inches of insertable length.  It is made of rigid silicone material, unlike a typical packer. This STP device can also be used for oral sex.  Users have declared that it creates a suction seal against the body. When applying suction it pulls the blood towards the tissues of the labia and clitoris, making it more sensitive.  It's an oral sensation.