The photo shows each of the connectors. Styles may vary.

#1 is a Straight 5/16" to 5/16" Connector.
 

#2 is a 1/4" to 5/16" adapter for application such as increasing tubing sizes from 1/4" to 5/16" a vice versa.
 

#3 is a 1/4" to 1/4" Straight connector.
 

#4 is a "Y" connector to connect three pieces of 5/16" ID tubing etc.
 

#5 is 5/16" on one end and tapered from less than 1/4" up to above 3/4" on the other end. This is excellent for connecting colon tubes to 5/16" tubing, etc.
 

#6 is 1/4" on one end and tapered from less than 1/4" up to above 3/4". This is excellent for connecting colon tubes to 1/4" tubing, etc.