Hex-1-yne, $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{C}\equiv \mathrm{CH}$, reacts with one equivalent of HBr in the presence of a peroxide. Ignoring E/Z isomerism, the major product is

Radical addition to a terminal alkyne follows the same logic as for alkenes. $\mathrm{Br}\cdot$ adds to the terminal carbon to give a vinyl radical at C-2 stabilised by the alkyl group, and H transfer from HBr gives $\mathrm{CH}{}_3(\mathrm{CH}{}_2){}_3\mathrm{CH}=\mathrm{CHBr}$ (1-bromohex-1-ene). With one equivalent, the dibromides do not form.