Joint Restraint Question (Watermain)

[questionsz]

Was wondering when normal MJ glands are used at fittings on a watermain (ex. A bend) vs. MJ joint gland with MJ follower gland and thrust bolts? When is one recommended vs the other?

Thanks in advance

 

[LittleInch]

Might help if you could add a drawing or say what exactly MJ stands for?

 

[bimr]