When using as a pair orriented in opposite directions on the shaft one can do "face to face" or "back to back" orrientation (contact angles pointing away giving a stiffer "fixed" condition for the end of the shaft and contact angles intersecting giving more of a "pinned" condition respectively). Bearings can also be spaced apart although not usually seen with back to back style instalations. For me the design called for back to back orientation (and no spacers). In that configuartion these bearings allowed for ~0.0015" to 0.0030" of linear lash in the shaft depending on the pair. Outer races are squeezed together firmly in the bearing blocks and inner races are squeeed together firmly on the shaft so the lash is definitely in the bearings themselves. This was a simple fix with shimstock washers cut to put between the inner races(not ideal but a livable fix in my aplication). I have never had to do this with the more expensive bearings that these are a clone of but these are 1 5 the price. Bottom line great for the price even with the shimming in my application. Will be using a lot of these if this first batch holds up well.