The FD-type studs are threaded almost to the top of the welding tip. Thus after welding the studs are threaded up to the wind collar, they are recommended to be used whenever full fastener length is needed.
Shear Connector are typically used in composite steel construction to tie the concrete slab to steel members and resist shear forces between the concrete slab and steel members.
The RD-type studs have a reduced weld base diameter. Thus they can produce a smaller weld collar diameter than other DA-type studs. The smaller weld collar allows it to use on smaller clearance holes application. But the strength of the assembly is determined by the reduced weld base.
The UD-type studs are designed to be used in the power generation industry, forging applications and locator pins stops, etc.