The tank lock fits through the cap of your oil tank and is secured in place with a padlock of your choice, preventing the cap from being removed.
The dimensions of the lock are: SPAN 22.5cm HEIGHT FROM PIN TO SHACKLE 10cm The shackle bar fits through one hole either side of the cap, these would normally be in the cap where a plastic bar was fitted when new.
If you have a screw cap on your tank it will be necessary to drill two 12mm holes through the cap and tank lip to accomodate the shackle.