You may alread find that fiber adapters have multimode or singlemode types. Singlemode fiber adapters is often more precise alignment of the tips of the connectors (ferrules). while multimode fiber adapters dont has that high precise alignment. So It is ok to use singlemode adapter to connect multimode cables, but do not use multimode adapters to connect singlemode cables. as it would increase insertion loss largely because of the alignment.

When it comes to multimode fiber optic adapters, You should pay attention to the core diameters between two fiber patch cables. As we know mutlimode has (50/125um or 62.5/125um core diameters), If you match 50/125um with 62.5/125um fiber,You will have high attenuation when 62.5/125um multimode fiber sending signals to 50/125um fiber.

What are the most used fiber optic adapters? Generally speaking,as SC LC FC ST fiber patch cord or pigtails are widely used in the fiber optic networks. so SC LC FC ST also becomes more and more popular in the fiber connectivity.Sometimes, When two fiber ends are different, You need a hybrid fiber optic adapter,such as SC to LC, SC-FC, SC to ST, FC-LC etc.When the connectors have differing ferrule sizes (1.25mm to 2.5mm), as found in LC to SC adapters, the adapters are significantly more expensive because of a more complicated design/manufacturing process.

To connect two fiber cables with two connectors, You can simply use a female to female fiber adapters,most of them are this type,addtionally, Some are male-female type, which typically plug into a port on a piece of equipment.