It may seems like simple homework question but it is industrial question with actual condition & I am struggling for the answer & also asked this question on other website but not get any reply. So ,please help me 'O' ring Internal Diameter(ID) ID=4 mm with tolerance is + & - 0.15mm. Tolerance as per in most of the standards. I design shaft of 4.0+0.15=4.15mm for maintaining minimum stretch of 0.00mm in any condition. If Shaft dia is 4.15mm & minimum 'O' ring ID is 4-0.15=3.85mm then 'O' ring stretch is 4.15-3.85=0.3mm. 'O' ring stretch percentage is 0.3/3.85 * 100=7.79 % > 5% alowable limit. Please tell me is there any other solution for this OR all the industries make compromise in stretch with small ID 'O' ring. I not gives any tolerance on shaft. If I will give then Stretch increase more & so intensify the problem.