The diminished scale contains a flat 3rd note (minor 3rd), a flat 5th note, and a double flat 7th note (compared to the major scale), so the step pattern is:
This pattern can be used when the root note of the diminished scale falls anywhere on the 5th string.
This pattern can be used when the root note of the diminished scale falls anywhere on the 6th string.
This is a useful scale to know when changing keys in lead work. The diminished scale has a unique property in that the root, b3rd, b5th and bb7th will share the same notes across the four keys that these notes contain, for example:
Therefore only 3 diminished scales are needed to cover all twelve keys.