Bought some Soffit Vents from Screwfix and they just will not go into the holes of the old ones. Are you supposed to cut the 'knobs' off or what???????
Are they these which require a 70mm dia cut out? https://www.screwfix.com/p/circular-soffit-vent-white-70mm-10-pack/68936 If so, what size are you existing cut outs?
Thinking the same, OP might need to enlarge exsisting hole, so might need a Starrett.A19 OOPS ARBOR allowing to use to different size hole saws. https://www.cromwell.co.uk/shop/cutting-tools/hole-saw-arbours/a19-oops-arbor/p/STT0508029T
From what I remember, all soffit vents are harder to get into solid board(rather than the hollow type soffit board). When cutting the holes in solid board, we used to wiggle the holesaw quite a bit, or it would be too tight to get in. The vents with lugs would break the lugs, and the screw in type would break the vent crossbars where it was too tight to screw in. But if you are trying the vent with lugs, turn it as you put it in, can help. Mr. HandyAndy - Really