Typical F Variety
Double engagement (F flex-flex) for parallel and angular misalignment
Single engagement (FFR flex-rigid) accommodates angular misalignment only and is great for floating shaft applications
Sector normal flange bolt patterns
FHD Form conventional for sizes ten by way of 30 (other sizes available on request)
Rigid-Rigid FRR Type
Designed for connecting two rigidly mounted shafts with no misalignment capability
Alloy Rigid-Rigid FARR Kind
Longer piloted hubs maintain rigidity and concentricity
Employed for cantilevered loads including gear boxes that hang off conveyor programs
Alloy steel offered for better power (FARR)
Mill Motor FMM Variety
Initially hub designed with longer universal hub on a single finish to accommodate straight or tapered shafts
Second 
hub bored to consumer specs
Conventional layout accommodates AISE Mill Motor frame sizes
Sleeves and second hub are conventional