Von Duprin NL Drive Screw 090074. Sold in Packs of 10. The 090074 NL Drive Screw is used on the Von Duprin 22, 98 and 99 Exit Devices to control the rotation of the key cylinder cam. This small set screw, screws into the back of the chassis assembly next to the receptor for the Rim Key Cylinder. The set screw measures 5/16" long by 3/16" diameter. Note: When the NL drive screw is left in back of device, the outside cylinder will function only as a Night Latch. The Night Latch function means the door can only be opened, but not dogged open with the key cylinder.