About the Lugs:
Heavy Duty Seamless Copper Starter Lugs combine pure copper construction with a seamless pad to provide the ultimate performance in strength, conductivity and corrosion resistance. The lug design and features a flared and chamfered barrel to facilitate cable insertion. These lugs 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.
The hole sizes on the lugs are sized to fit the bolt of the same size so a 5/16 hole lug will fit a 5/16 inch bolt etc. The 5/16 lugs will also fit M8 metric as will the 3/8 lugs fit the M10 size metric bolts.
About the Adhesive Heat Shrink Pieces:
The Adhesive Heat Shrink provided which is optionally available to you comes in Black or Red and is pre-cut into 1.5" long pieces, the prefect length to seal the lug after it's been crimped or soldered to the wire. 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 lugs.
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 Larger
A 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.