The present invention relates generally to medical/dental devices for fixing bone fractures, anchoring of bones, or anchoring of prosthetics to bones. The device generally relates to molly bolts, expandable screws, or devices/screws with expansion or locking mechanisms. More particularly, the present invention concerns an implant assembly which includes a tubular body portion that can be positively secured within a bore in a bone or prosthetic by expander mechanism at both ends of the tubular body portion.