Danville Lead Wire is spool lead wire used for weighting flies. Size of wire is selected based on thickness of the hook wire. Small is for size 10-16, Medium is for size 8-12, Large is for size 4-6-8. Obviously this contains lead which may be hazardous, please use caution around small children and wash hands after using. Some regions prohibit use of lead wire such as Yellowstone Park. Loon protected areas in NY allow use of lead wire. Please note: due to supply chain issues we may substitute brands. Any substitutions are identical in price, size and materials.