Designed for greater key control, the 1870 Cylinder-Operated Flushbolt prevents accidental locking of the inactive leaf of narrow stile aluminum paired doors. May be installed to lock at threshold or at header. Function: Designed for use instead of conventional flip-lever operated flushbolts, 1870 Cylinder-Operated Flushbolts give building management key control of the inactive leaf of paired narrow stile aluminum doors. Prevents casual locking of the inactive leaf by unauthorized persons. Uses same basic over-center action mechanism as MS® pivoted bolt deadlocks. Recommended for installation at both top and bottom of inactive door with MS1850S MS Deadlock in active doorfor greatest security. May be installed to lock at threshold or at header. Operation: 360° turn of key throws or retracts the hex-section bolt. Key can be removed only when bolt is in a positively locked or unlocked position. Lock accepts any standard1" [25.4 mm] length, 1-5/32" [29.4 mm] diameter mortise cylinder with MS® cam such as the 4036 Mortise Cylinder or thumbturn such as the 4066Thumbturn, available separately. Lock accepts cylinder from either or both sides. This listing: part 1870-20-628 31/32"BS, in 628 Clear anodized finish.