Locking filler cap

A lockable assembly for a tank filler opening comprising:

• a cap having a top with a first outside diameter, a thread on a second outside diameter adapted to engage a complementary thread on a first inside diameter of said tank filler opening, a receptacle defined by a second inside diameter in said top, and a groove in said receptacle, below said top, having a third inside diameter;
• an insert having a third outside diameter, a substantially planar shield having a fourth outside diameter, wherein said shield comprises the upper surface of said lockable assembly, and wherein said shield covers at least a portion of said top, a first opening extending longitudinally through at least a portion of said insert, and a second opening extending laterally through at least a portion of said insert from said first opening to said third outside diameter, said second opening being axially aligned with said groove, wherein said second inside diameter of said receptacle provides a complementary fit for said third outside diameter of said insert, and wherein said shield is flushmount with the vicinity of said tank filler opening when the insert is placed inside said cap;
• and
• an interchangeable lock within said first opening having a latch, wherein said latch is operatively moved by said lock from said second opening to engage said groove, and wherein said latch is selected from the group consisting of:
• bolts, pins, tongues, ball bearings, and cams.