Hi everybody, i am confused about model numbers of this watch, automatic or with battery no matter but what's the difference between 8926 and 8926 OB?

8926 is automatic, o.b. is also automatic but has a bezel that looks more like an old Rolex. Same watch otherwise

Does this watch Have a NH35A movement? Description doesn't say.

Should be a seiko nh35 Japanese movement.

Does the Invicta 8926 Pro Diver have a screw down crown?

Hello,Thank you very much for your inquiry. Yes, the Invicta 8926 does feature a screw down crown. Please let us know if there are any additional questions or concerns regarding this model.Thank you,Discount Watch Store Customer Service

Does the second hand works as in a smooth sweeping motion similar to automatic Rolex motion or jumping quartz motion?

Sure, you can say that the smoother second hand sweep (of a Rolex Submariner for example) is due to the far higher price paid, and that's not untrue. But the more specific cause of this effect (as I understand it) is the faster rate at which the Rolex movement operates (also true of certain other premium mechanical movements from various watchmakers). This rate is usually expressed as BPH (Beats Per Hour) and for Rolex-class mechanical watches the typical rate is 28,800 BPH which equates to 8 mini-ticks of the second hand for each actual second (giving the impression of very "smooth" movement). The more reasonably priced automatic movements (like the SEIKO-designed NH35A as used in many watches) run at 21,600 BPH or 6 mini-movements/ticks of the second hand per actual second (giving the impression of a slightly less smooth-moving second hand than with the 8 mini-ticks per second versions).