These are new stainless Shadow/Spirit/Spur caliper pistons.  They are guaranteed to never rust.  
The largest one (CD4072/CD5737/CD5844) is for all front calipers.
The smallest one (CD4074) is for all rears.  
The medium piston (CD4073/CD6283) is for the rear on early Shadows with the master cylinder circuit.  These cars have two small and two medium pistons per rear caliper.  
Later cars without master cylinders have 4 small pistons per caliper.