Those are basic part numbers and the actual part number depends on the type of column (fixed or tilt), vehicle type (F100-350, U150, etc), when manufactured, etc. 3D681 is a Retainer Assembly and only on a fixed column, 3517 is a Bearing Assembly and my parts catalog says it must be purchased locally ( a standard bearing apparently), 3518 is a Sleeve (steering column tube bearing) and has two possible part numbers.
Possible Part numbers are 3D681 - P/N E0TZ 3D681-A (Black plastic - round sleeve type) and P/N E0TZ 3D681-B (Red plastic - round ring type). 3517 (Bearing assembly) - P/N D4TZ 3517-A but a note says you have to purchase it locally ( a standard bearing). 3518 (Sleeve, steering column tube bearing) P/N D1AZ 3518-A upper bearing retainer w/fixed column, P/N D8BZ 3518-A lower bearing retainer.
Good luck,
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