Priming volume:

Is how much blood needs to fill dialyzer capillaries, it consider as dead blood volume. it is varies among dialyzers, as a role of thumb, more priming volume, more surface area, more clearance and more UF coefficient among the same dialyzer group. It is good for children and small size adult

Surface area:

It how much the dialyzer capillaries cover square area, it is correlated by the number and size of capillaries.
Higher surface area the other dialyzer specification will be high like UF, priming volume, and clearance among same dialyzer group

Inner diameter:

It is the dialyzer capillaries internal diameter.
It is important for the blood to pass freely through the capillaries
Most dialyzers have inner diameter 200 micro.
Some new dialyzer designed 250 micro

Wall thickness:

Almost all dialyzer have wall thickness 25 between 50 micro. Less wall thickness promote diffusion of larger molecules

Bores size:

Reflect how much freely the particles move across the membrane, larger bores size promote diffusion of larger molecules
The freely passage depend on particles atomic weight called Dalton, more particles Dalton less passages.
Low Flux dialyzers have small bores while the high Flux usually have large bores to enhance clearance and to remove high weight molecules