A cylindrical rod-like device used as a precision reference to provide the correct spatial distance between an an intramedullary bone nail (femoral, humeral, tibial) to which it is interfaced, and an aiming arm, joining the two in a relative position. This procedure is performed to set-up the aiming arm prior to surgery; the set-up is dismantled and then reconnected after implantation of the nail with this device (the spacer) which is percutaneously introduced into a selected hole in the bone nail. It is typically made of high-grade stainless steel or synthetic materials. Several reference spacers may be used for this procedure. This is a reusable device.