It is a type of two-component sealant made from cyanoacrylate glue and an activator spray. This product is used for quickly bonding parts together. Attention Major Consumers of 123 sealant: You can purchase one 600ml sealant (which includes two 100g glues and one 600ml spray, twice the weight of the 400ml spray) at a much better price instead of buying two 400ml sealant.