If this is a self feed string, double the string omto the spool in the direction the spool turns, feed each piece out the opposite holes, cut to length approximately, the shield will probably have a blade to cut the proper lengh when if feed out.
If this is the large two wheeled job, feed in to the large loop from the oursides, and back out the inside loop cut to lenght. After you figure the lenght needed, it's a good idea to make several that length to replace later, thus you can feed into both outside loops and back into the inside, both at once.
Cliff Collins 66-81-182-53.nocal.dialup.o1.com, September 2006