Each time the bearer fights, it can make one (and only one) attack with this weapon. Make D3 hit rolls for this attack instead of one. This is in addition to the bearer’s attacks.
Tyranid thresher scythe.
You can re-roll hit rolls of 1 for this weapon. If the bearer has more than one pair of monstrous scything talons, it can make 1 additional attack with this weapon each time it fights.
Scything talons. Emphasis mine on both.
Thresher scythe reads to me that you make D3 rolls to hit, but if any hit then you score one (1) hit, so you have an increased chance of hitting once.
Why would it not say 'Each time the bearer fights, it can make D3 attacks with this weapon. This is in addition to the bearer's attacks.'
Weapons that give you additional attacks say so and make no mention of hit rolls.
Am I wrong? I think I'm wrong but it's worded oddly, IMO.