Abstract: Undesired access to a fuel oil fill pipe having a threaded cap fitting and a threaded cap is prevented by a fuel oil fill-port locking mechanism having: a coupling mateable with the fuel oil fill pipe; a nipple mateable with the coupling the cap fitting; an oil fill-port cover which denies access to the cap; a pair of oppositely disposed apertures in the coupling and a pair of alignable apertures in the cover; a lock pin sized to fit through the aligned aperture; a transverse bore through one end of the lock pin; and a lock pin stop at an opposite end of the lock pin. The cap and the cap fitting are removed from and the coupling is threaded onto the fuel oil fill pipe, the nipple is threaded into the coupling, then the cap fitting threaded into the nipple and the cap threaded into the cap fitting.

Abstract: Undesired access to a fuel oil fill pipe having a threaded cap fitting and a threaded cap is prevented by a fuel oil fill-port locking mechanism having: a coupling mateable with the fuel oil fill pipe; a nipple mateable with the coupling the cap fitting; an oil fill-port cover which denies access to the cap; a pair of oppositely disposed apertures in the coupling and a pair of alignable apertures in the cover; a lock pin sized to fit through the aligned aperture; a transverse bore through one end of the lock pin; and a lock pin stop at an opposite end of the lock pin. The cap and the cap fitting are removed from and the coupling is threaded onto the fuel oil fill pipe, the nipple is threaded into the coupling, then the cap fitting threaded into the nipple and the cap threaded into the cap fitting.