What closer do I use for an exterior gate


Most Panic devices are not designed for exterior applications. As with any mechanical device, exposure to the elements may affect the operation and life of the device and/or finish an...
A 4110 with AVB (advance variable back check) would be recommended. Using a SCUSH (Spring Cush) arm will also help minimize shock to all door hardware.
Electric strikes are not water proof an not recommended for exterior application especially gates.
The LCN closers are not designed nor intended to be exterior mounted in the elements.  
The 6000 series electric strikes are commonly used on exterior doors but they are not waterproof and are NOT recommended for outside such as on a gate with no protection from the elements.
The 4041/4040XP and 4040SE closers cylinders are "NOT" the same. The 4041/4040XP cylinder has an adjustable size 1-6 spring. The 4040SE cylinder has an adjustable size 2-4 spring. The 4041/404...
The Falcon SC60, SC70, and SC80 series closers all use the same arm options. The SC91 series uses a different arm from the rest.