IDoring = 7.5 mm CSoring = 1 mm   MIrrorDiameter = 7.95 mm GrooveDiameter= 0.370in GlandWidth=0.058in STRETCH The percent stretch, usually simply called the stretch, is defined by the diameter of the hardware minus the O-ring inner diameter (ID), all divided by the O-ring ID. The diameter of the hardware value represents the diameter the O-ring is being stretched about. For male designs, this diameter is the groove. For female designs, it is the rod. For face seals, this can be the ID of the groove. This formula can also be used for installation stretch where the hardware diameter is the outer diameter of the installation tool or the maximum diameter that the O-ring must pass over for installation.  Dhardware=MIrrorDiameter  = 7.95 mm stretch=(Dhardware-IDoring)/IDoring  = 0.06 Ideal: 0-5% SQUEEZE To form a robust seal, adequate compression or squeeze is a critical consideration. Compressing the seal energizes it, and the O-ring pushes back on the mating surfaces. This contact force between the O-ring and hardware creates a seal. Squeeze is calculated by the cross-section diameter minus the gland depth, all divided by the cross-section diameter. Note that in this calculation, the gland depth is the distance from the bottom of the groove to the mating surface. This accounts for any clearance gap. dCS=CSoring  = 1 mm tGlandDepth=(GrooveDiameter-MIrrorDiameter)/2  = 0.0285 in Squeeze = (dCS-tGlandDepth)/dCS  = 0.276 Ideal: 22-32% VOLUME FILL The final essential criterion for O-ring design is volume fill, also called gland fill. The compressed O-ring must have extra space within the groove without overfilling the groove. Volume fill is the O-ring volume divided by the gland volume. NOTE: Since the volume of the gland is calculated by mulitplying the area of the gland by the circumerence of the gland and the volume of the oring is calculated by multiplying the aread of the oring by the circumference of the centerline of the oring and both circumferences are basically equal when the oring is compressed in the gland, the Volume Fill is the quotient of the areas. OringArea=(pi/4)*CSoring^2  = 0.785 mm^2 GlandArea=tGlandDepth*GlandWidth  = 0.00165 in^2 VolumeFill=OringArea/GlandArea  = 0.736 Ideal: 60-90%