Hi,
there should be an accuracy grade mentioned in the advertising material.
C7- is the most common rolled ballscrew grade, 50um over 300mm and 35um cyclic error.
There are T grades, T for transport and are not good enough for CNC, likewise there are P grades, P for positioning, but again not really good enough for CNC.
Then there are C5, C3...through C0 grades. C5 is the entry level ground screw grade, 18um per 300mm, 7 um cyclic error. A big improvement over C7, but a HUGE price
increase.
If you paid $150 for a 20mm C7 rolled screw with bearing blocks , expect to pay $1500 for the same size C5 ground grade....yes that's right about TEN times the price.
C3 grade is for top end CNC machines and more expensive than C5s. C1 and C0 are for CMM's and semiconductor equipment. C1 and C0 are special order from the factory
and I have no idea how much they cost, tens of thousands would be my guess.
I bought three 32mm BNFN (double nut) THK C5 ballscrews second hand for my new mill. I can't afford new C5s but good second hand C5s are about the same price as new C7s.
Craig