When #d=0# inches the situation will be represented by the modified figure as shown above. The distance across the top of the worm thread then will be #PR#
Now #PR =2PQ= (2PQ)/(OQ)xxOQ#
#=>PR = (2PQ)/(OQ)xx(QC+CQ)#
#=>PR = (2PQ)/(OQ)xx(QC+(CQ)/(CN)xxCN)#
#=>PR = (2PQ)/(OQ)xx(CN+(CQ)/(CN)xxCN)#
#=>PR = (2PQ)/(OQ)xxCN(1+(CQ)/(CN))#
#=>PR = 2tanthetaxx0.75(1+csctheta)#
#=>PR = 1.5(tantheta+tanthetaxxcsctheta)#
#=>PR = 1.5(tantheta+sectheta)#
#=>PR = 1.5(tan15^@+sec15^@)~~1.95# inch