About the Splices:Heavy Duty Seamless Copper Butt Splices combine pure copper construction with tin plating to provide the ultimate performance in strength, conductivity and corrosion resistance. The butt splices feature a flared and chamfered barrel to facilitate cable insertion. These butt splices are sized and designed to work with flexibly stranded copper wire and cable such as welding cable, marine battery cable, UL Listed battery cables, SAE battery cables, entertainment cable, diesel locomotive cable, and other similar flexible cables. UL Listed/CSA Certified Pure Copper - 99.9% Conductive ETP Copper Tin Plated to Resist Corrosion Various Sizes available You choose the size, color of heat shrink and quantity Here are the crimp die color codes to use with each size: (you may use hammer style crimpers as well)8 AWG RED 6 AWG BLUE 4 AWG GRAY 2 AWG BROWN1/0 AWG PINK2/0 AWG BLACK About the Adhesive Heat Shrink Pieces:The Adhesive Heat Shrink provided is available in Black or Red and is pre-cut to the prefect length to seal the splice after it's been applied to the wires. The adhesive heat shrink has a glue lining that will melt and seal the connection against dirt and moisture. This is a dual wall 3 to 1 shrink tubing so it will hold very well and the diameter has been chosen to best fit your splice. Also keep in mind the sizes of cables go from smaller to larger as so: 18 AWG Smaller 16 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG LargerA side note about copper clad aluminum cable some of you are using...If you are using cheap CCA wire (copper clad aluminum) the sizes of that aluminum cable will be larger than copper since aluminum can't carry the same current as copper and therefor the cable size they use, while the same in name, will be larger than the copper awg size and will likely not fit in the same size lug. You'll need a size or maybe 2 larger...just ask us and we can help you figure it out. Again, these quality lugs are designed to be used on quality copper wire only.