Critical to positive protection during well service operations is the selection of the correct flotube and maintaining the optimum clearance between the flotube and the cable outside diameter.

The flotube used must be matched to the wireline in use, considering any wear on the wireline.  Thus, for each nominal wireline size there is a choice of tubes.

NOV recommends a clearance of 0.003 to 0.005 in between flotube ID and wireline OD, with a maximum of 0.008 in when line and tube wear out.