[not worth a tinker's damn] or not [worth a tinker's dam] […]

[nothing to it] {adj. phr.} Presenting no serious challenge; easily accomplished. […]

[null and void] {adj.} Not worth anything; no longer valid. * […]

[number one] (2) {adj. phr.} 1. Of first rank or importance; […]

[numpty] {adj.} Incompetent or unwise person.

[nuts or nutty] {adj.} Crazy or insane.

[nutty as a fruitcake] {adj. phr.}, {slang} Very crazy; entirely mad. […]

[odds-on] {adj.}, {informal} Almost certain; almost sure; probable. * /Ed is […]

[of a piece] {adj. phr.} Of the same kind; in line. […]

[of age] {adj. phr.} 1a. Old enough to be allowed to […]