The paper proposes a methodology to compute reliability of the screw plant. A screw plant consists of four subsystems A, B, C, D working in series namely heading machine, slotting machine, thread rolling machine and polishing machine. Subsystem A is supported by standby units having perfect switching over device and subsystem C has two units in parallel redundancy and remaining two subsystems B and D are subjected to major failure only. For system configuration and establishment of the model we prefer Boolean algebra method and orthogonal matrix method has been used for reliability calculation. Reliability of the Screw Plant has been estimated when the failure rate expressed by weibull and exponential time distribution. Mean time to failure has also been determined for exponential time distribution, which is also a relevant characteristic of reliability.