At the Mennonite Quilt Center in Reedley CA a group of local ladies come together every Monday to tie comforters . Comforters is what they called the ones that are tied and quilts the ones that were hand quilted. They usually used 12oz Hobbs poly.
Buying for a group it is less expensive to buy by the roll...I would wait until JoAnn's has a 50% discount. They would tie in each corner of a 5" block and if a block was bigger they will tie also in the center of the block...any way just so the the ties are not too far apart. They only use crochet thread.