twehr is right. Here are the differences I noted with crosshairs:
Focusble:
- Silver
- Fatter and longer (I can measure if DX doesn't have the measurements)
- Sharper when focused
- Crosshair rotates when focusing
- Shorter depth of field (so crosshair is fuzzier as you move away from the focal distance)
Fixed:
- Brass
- Smaller and lighter
- Not quite as sharp as the focusable one at its focal distance
- Much sharper than the focusable one over large distances (large DOF)
When I bought line lasers I bought only fixed ones (being familiar with the points above) because my purpose for dual lines was to use them on something like a drillpress where I wanted the crossing point to align with the tip of the drillbit at any table distance.