Okay this is where it gets confusing. There are many different lug standards. The two most common for marine & trucking use are the Flared Starter Lug as seen on the left and the Heavy Duty Power Lug as seen on the right. Different manufacturers have slightly different names but FTZ calls them Power Lugs and Quick Cable calls them "Magna Lugs". It is important to note that the lug on the left is for 4 GA wire and the lug on the right is ALSO for 4 GA wire.
*WARNING These lugs use DIFFERENT DIES. When buying a crimp tool PLEASE be very careful you buy the right tool. There are many tools out there marked for 6 GA to 4/0 GA wire that will not work correctly and do not come with the proper dies. You are then left guessing which dies to use for the flared starter lugs and which tool for the heavy duty lugs.
The right tool will have labels for "Flared Starter Lugs" and for "Heavy Duty Power Lugs". There are only two relatively affordable tools I know of to meet this lug crimp standard and they are the FTZ and the Quick Cable crimp tools. Most of the other tools out there are made for the industrial lug standard.
Heavy Duty Power Lugs will always be marked with a color code and have two letter embossed or stamped into the lug. If your "heavy duty" lugs do not have these colors and letters they are very likely not the proper size for the dies.
Many People have asked me where they can get FTZ lugs from. The answer is Sailboatowners.com
FTZ Heavy Duty Power Lugs
FTZ Flared Starter Lugs