Repair links are actually used for a lot more than just chain repair. They show up in a lot of places, such as lift gate chains, trailer safety chains, dog leashes, sports and recreation, household use and more. Some of the more heavy-duty types, like Crosby S-249 Twin Clevis Links, have high load ratings and work well with Grade 70 chain systems. Other types, like Zinc-Plated Spring Snap Links, are rated for much less yet are very popular and used all across the world. No matter how you plan to use these various links, just be sure to note the capacity of each individual link as their ratings vary greatly from one to the next. Also, please note these links are not to be used for overhead lifting, fall protection or any other critical applications.
If you're working with Grade 80 or Grade 100 Chain, then be sure to use compatible couplers; Gunnebo Grade 100 G Links and Crosby S-1325A Grade 100 Couplers are both popular choices. They go together easily, and while they stay together very securely while in use, you can disassemble them if needed by using a hammer and punch. They work perfectly with most Lifting Grade Chains.