Pitch diameter tolerance of external thread of plastic parts Manufacturing tolerance of threaded ring cavity, for pitch diameter, =475 and for major and minor diameters, 8=A/4 Computation for the Dimension of Threaded Core dn=[dm(1+k)-△]- d=d(1+k)-△] d=[dn(1+k)-A]。 Wherein: d-D n of pitch diameter of threaded core; d diameter of threaded ds- Dimension of minor diameter of threaded core dpm-Nominal dimension of pitch diameter of plastic parts'internal thread dpl-Nominal dimension of major diameter of plastic parts'internal thread: dps ts’ internal thread Tolerance of pitch diameter of plastic parts'internal thread Manufacturing tolerance of threaded core, for pitch diameter, S =A/5,and for major and minor diameters, 8=A/4 3)Computation for Working Dimension of Screw Pitch P=P(1+k)±6/2 (2-8) Wherein: Pp- Nominal dimension of screw pitch of plastic thread parts; 6 ng P-Dimension of screw pitch of threaded ring cavity or threaded core Usually, when the number of threads is less than 7-8, it is not necessary to count the working dimension of screw pitch; instead it can be redeemed through the engagement clearance of thread Table 2-1: manufacturing tolerance of threaded core or threaded ring cavity Diameter of Thread Length of Fit oor ng toleranced Manufactu 12~22 >12~20 24~66 4. Examples of Computation Refer to Fig2-8 for the structural dimension of plastic parts and corresponding cavity structure, wherein the plastic parts are made from polypropylene, the shrinkage is 1%-3%. The dimension of cavity and core is to be calculated ig 2-8: plastic parts and corresponding cavity and coreΔ —— Pitch diameter tolerance of external thread of plastic parts; δ —— Manufacturing tolerance of threaded ring cavity, for pitch diameter,δ = Δ / 5 , and for major and minor diameters, δ = Δ / 4 . 2）Computation for the Dimension of Threaded Core δ δ δ − − − = + − Δ = + − Δ = + − Δ [ 1 ] [ 1 ] [ 1 ] （ ） （ ） （ ） d d k d d k d d k s ps l pl m pm （2-7） Wherein: dm —— Dimension of pitch diameter of threaded core; dl —— Dimension of major diameter of threaded core;； ds —— Dimension of minor diameter of threaded core; dpm —— Nominal dimension of pitch diameter of plastic parts’ internal thread; dpl —— Nominal dimension of major diameter of plastic parts’ internal thread; dps —— Nominal dimension of minor diameter of plastic parts’ internal thread; Δ —— Tolerance of pitch diameter of plastic parts’ internal thread; δ —— Manufacturing tolerance of threaded core, for pitch diameter,δ = Δ / 5 , and for major and minor diameters, δ = Δ / 4 . 3）Computation for Working Dimension of Screw Pitch P = P（p 1+ k）± δ / 2 （2-8） Wherein: Pp —— Nominal dimension of screw pitch of plastic thread parts; δ —— Refer to Table 2-1 for the manufacturing tolerance of screw pitch; P —— Dimension of screw pitch of threaded ring cavity or threaded core. Usually, when the number of threads is less than 7~8, it is not necessary to count the working dimension of screw pitch; instead it can be redeemed through the engagement clearance of thread. Table 2-1: manufacturing tolerance of threaded core or threaded ring cavity Diameter of Thread Length of Fit Manufacturing Toleranceδ 3 ~10 12 ~22 24 ~ 66 ~ 12 >12 ~ 20 >20 0.01 ~ 0.03 0.02 ~ 0.04 0.03 ~ 0.05 4. Examples of Computation Refer to Fig.2-8 for the structural dimension of plastic parts and corresponding cavity structure, wherein the plastic parts are made from polypropylene, the shrinkage is 1％-3％. The dimension of cavity and core is to be calculated. Fig.2-8: plastic parts and corresponding cavity and core