--- title: "Classify fits from given limits of size" subject: "Metrology" chapter: 9 key: "semester_3/metrology:classify-fits-from-limits" source: https://www.bctengineer.com/q/semester_3/metrology/classify-fits-from-limits site: BCT Engineering --- # Classify fits from given limits of size Metrology · Chapter 9: Limits, Fits and Tolerance - Asked in: year not given, 6 marks - Video: [Limits and Fits: The ISO System](https://www.youtube.com/watch?v=wvVMs2BZdeU) — Tabletop Machine Shop - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/metrology/classify-fits-from-limits - Whole chapter: https://www.bctengineer.com/md/semester_3/metrology/chapter-9 ## Question The limits of size of three hole-shaft pairs are given below. For each, find the tolerances, the maximum and minimum clearance (or interference), and state the type of fit. (a) Hole 30.000 to 30.021 mm; shaft 29.967 to 29.980 mm. (b) Hole 50.000 to 50.025 mm; shaft 50.002 to 50.018 mm. (c) Hole 25.000 to 25.021 mm; shaft 25.035 to 25.048 mm. ## Short answer (a) Clearance fit: hole tolerance 0.021 mm, shaft tolerance 0.013 mm; clearance 0.020 to 0.054 mm. (b) Transition fit: hole tolerance 0.025 mm, shaft 0.016 mm; +0.023 to -0.018 mm. (c) Interference fit: hole tolerance 0.021 mm, shaft 0.013 mm; interference 0.014 to 0.048 mm. ## Answer Use: $C_{max} = $ hole max $-$ shaft min; $C_{min} = $ hole min $-$ shaft max. A negative value is interference. | | (a) | (b) | (c) | |---|---|---|---| | Hole tolerance | $0.021$ | $0.025$ | $0.021$ | | Shaft tolerance | $0.013$ | $0.016$ | $0.013$ | | $C_{max}$ = hole max - shaft min | $30.021 - 29.967 = +0.054$ | $50.025 - 50.002 = +0.023$ | $25.021 - 25.035 = -0.014$ | | $C_{min}$ = hole min - shaft max | $30.000 - 29.980 = +0.020$ | $50.000 - 50.018 = -0.018$ | $25.000 - 25.048 = -0.048$ | | Fit type | Clearance | Transition | Interference | #### Results - **(a) Clearance fit:** the clearance always lies between 0.020 mm and 0.054 mm. The shaft is always smaller than the hole, so it is a running fit (it matches 30 H7/f6). - **(b) Transition fit:** the maximum clearance is 0.023 mm and the maximum interference is 0.018 mm. Depending on the actual sizes, the assembly may have clearance or interference. It is used for accurate location (it matches 50 H7/k6). - **(c) Interference fit:** the minimum interference is 0.014 mm and the maximum is 0.048 mm. It is always a press fit (it matches 25 H7/s6). All three pairs are on the hole basis, as the lower limit of the hole equals the basic size in each (lower deviation zero). **Answer: (a) clearance, 0.020 to 0.054 mm; (b) transition, +0.023 to -0.018 mm; (c) interference, 0.014 to 0.048 mm.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How are Cmax and Cmin found from limits of size? A. Cmax = hole max - shaft max; Cmin = hole min - shaft min B. Cmax = hole max - shaft min; Cmin = hole min - shaft max C. Cmax = shaft max - hole min; Cmin = shaft min - hole max D. Cmax = hole tolerance + shaft tolerance only Answer: B. The largest gap is the biggest hole minus the smallest shaft; the smallest gap is the smallest hole minus the biggest shaft. A negative result means interference. (Key point: Clearance formulae) 2. Hole 30.000-30.021, shaft 29.967-29.980. What is the fit? A. Transition fit, +0.054 to -0.020 mm B. Interference fit, 0.020 to 0.054 mm C. Clearance fit, 0.020 to 0.054 mm D. Clearance fit, 0.013 to 0.021 mm Answer: C. Cmax = 30.021 - 29.967 = 0.054 and Cmin = 30.000 - 29.980 = 0.020, both positive. (Key point: Pair (a)) 3. Hole 50.000-50.025, shaft 50.002-50.018. What is the fit? A. Clearance: 0.023 to 0.018 mm B. Interference: 0.023 to 0.018 mm C. Transition: Cmax = +0.043, Cmin = -0.018 mm D. Transition: Cmax = +0.023, Cmin = -0.018 mm Answer: D. Cmax is positive (50.025 - 50.002) and Cmin is negative (50.000 - 50.018), so the sign changes: a transition fit. (Key point: Pair (b)) 4. Hole 25.000-25.021, shaft 25.035-25.048. What is the fit and its interference range? A. Interference fit, 0.014 to 0.048 mm B. Clearance fit, 0.014 to 0.048 mm C. Transition fit, +0.014 to -0.048 mm D. Interference fit, 0.021 to 0.048 mm Answer: A. Both Cmax = -0.014 and Cmin = -0.048 are negative, so the shaft is always larger: minimum interference 0.014, maximum 0.048. (Key point: Pair (c)) ## Related in Metrology - [Limits of a 40 H7/g6 hole-shaft fit](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Afit-40-h7-g6-calculation) — Metrology, chapter 9 - [Basic terms of limits, fits and tolerances](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Alimits-fits-terminology) — Metrology, chapter 9 - [Clearance, transition and interference fits](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Atypes-of-fits-with-examples) — Metrology, chapter 9 - [Hole basis and shaft basis systems](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Ahole-basis-vs-shaft-basis) — Metrology, chapter 9 ## Related in other subjects - [Limits, fits and tolerance calculation](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Alimits-fits-tolerance-numerical) — Manufacturing and Production Processes, chapter 3 - [Assembly constraints and tolerance fit calculation](https://www.bctengineer.com/question.md?key=semester_4%2Fcomputer_aided_design%3Aassembly-constraints-tolerance-fit) — Computer Aided Design, chapter 5 - [Settling tank 30 m x 3 m, 0.03 mm at 25°C; 0.025 mm at 20°C](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ased-k72) — Water Supply Engineering, chapter 6, asked 3× - [Minimum spacing for 30 mm conductors (m = 0.95)](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Acorona-spacing-30mm-0-95) — High Voltage Engineering, chapter 5, asked 4×