Sentencing the two men who sent parcel bombs to Celtic manager Neil Lennon, trial judge Lord Turnbull said their actions were "incomprehensible".
Trevor Muirhead and Neil McKenzie were convicted last month following a five-week trial at the High Court in Glasgow.
The jury heard that McKenzie told police he learned how to make a hoax bomb after seeing it on the 1980s TV show The A-Team. Giving evidence during the trial, Lennon said he was left "very disturbed" after finding out he had been targeted.
The assault plot centred on four suspicious packages, all of them non-viable, which were discovered last spring.
A second device sent to Lennon at Celtic's training ground in Lennoxtown, was intercepted at a sorting office in Kirkintilloch last year when a postman spotted a nail protruding from it.