Strap-On
You will be surprised at the variety of strap-on designs
available today. Some models will have a permanent dong attached to
it and others will have interchangeable designs. The
interchangeable designs also vary.

Some will have a vac-u-lock design. This is a special plug
that is inserted through the back of the pelvic portion of the
harness and snaps in place. Then insert the plug into a
specially made dong attachment that has a hollow core at the base.
The harness is now pinched between the plug and the dong. The dong
will stay in place because of the vacuum suction that was created
when the plug was inserted into the hollow dong. The only draw back
to this design is the harness will only accommodate attachments
specifically made for that harness.
The other type is the o-ring type. The o-ring type has a ring
that is held to the harness by snaps. Insert any dong or vibrator
that has a flared base or testicles through the o-ring and snap the
ring into place on the harness. There is much more potential for
variety with the o-ring type than with the plug type.
When comparing one strap-on to another look at the difference in
attachment types and note how the harness secures to the
wearer.