Karandeep Singh, 19, of no fixed abode, was convicted of robbery and section 20 grievous bodily harm following a trial at Reading Crown Court that lasted six days.
Satwant Singh, 34, also of no fixed abode, was found guilty of robbery.
The verdicts were unanimous.
Satwant Singh was sentenced to three years and eight months in prison for robbery on October 10, while Karandeep Singh returned to the same court on December 17 and was jailed for a total of four years and eight months.
He was also sentenced to a further 14 days in prison for failing to appear at court, to be served consecutively.
On May 25 2023, Satwant and Karandeep Singh entered the branch of Wickes on Farnham Road in Slough.
Satwant attempted to leave the store with a metal spirit level without paying and when a staff member attempted to stop him, he dragged him out of the store by his collar.
Outside the store, an altercation followed which resulted in Karandeep Singh taking hold of the spirit level and hitting the victim, a man aged in his twenties, to the back of his head, causing him injuries that required medical attention.
Another staff member also sustained minor injuries.
Both offenders then left the store with the spirit level.
They were both arrested for robbery in June 2023 and subsequently charged, Satwant on June 3 2023 and Karandeep on June 10 2023.
The trial was due to start in on October 1 this year, but was delayed as Karandeep failed to appear at court.
Investigating officer Detective Constable Lauren Rose of the Slough Priority Crime Team said: “After a lengthy investigation and court process, the Singhs have now been sentenced for this violent robbery.
“Karandeep Singh’s sentence reflects the seriousness of the offence as he also caused head injuries to the main victim in this case.
“I am pleased that the court have sentenced both of them to significant prison sentences, and I hope that this outcome allows the victims to put their ordeal behind them.
“I am also pleased that Karandeep was further sentenced for failing to attend court, which might make him think twice before attempting to evade justice again.”