--- title: "Hole basis and shaft basis systems" subject: "Metrology" chapter: 9 key: "semester_3/metrology:hole-basis-vs-shaft-basis" source: https://www.bctengineer.com/q/semester_3/metrology/hole-basis-vs-shaft-basis site: BCT Engineering --- # Hole basis and shaft basis systems Metrology · Chapter 9: Limits, Fits and Tolerance - Asked in: year not given, 5 marks - Video: [Hole Basis System and Shaft Basis System](https://www.youtube.com/watch?v=egSMlg3TgUg) — Gear Institute Mechanical Engineering Videos - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/metrology/hole-basis-vs-shaft-basis - Whole chapter: https://www.bctengineer.com/md/semester_3/metrology/chapter-9 ## Question Differentiate between the hole basis system and the shaft basis system of fits. Why is the hole basis system more commonly used? ## Short answer Hole basis: zero lower deviation hole (H), varying shaft. Shaft basis: zero upper deviation shaft (h), varying hole. Hole basis is preferred because holes require fixed dedicated tools (reamers, broaches); one H hole reamer serves many fits, reducing tool costs, while shafts are easily machined to any size. ## Answer In the **hole basis system** the basic size is the minimum limit (lower limit) of the hole, so the lower deviation of the hole is zero (letter H). Different fits are obtained by varying the size of the shaft. In the **shaft basis system** the basic size is the maximum limit of the shaft, so the upper deviation of the shaft is zero (letter h). Different fits are obtained by varying the size of the hole. | Point | Hole basis | Shaft basis | |---|---|---| | Fixed member | Hole (H, lower deviation 0) | Shaft (h, upper deviation 0) | | Varying member | Shaft | Hole | | Example | 40 H7/g6, H7/k6, H7/p6 | 40 G7/h6, K7/h6, P7/h6 | | Tools for the fixed part | Standard reamers, broaches and plug gauges are limited in number | Standard shafts, ground bars | | Cost | Lower for general use | Higher: many hole sizes need many reamers | | Used | Machine tools, general engineering | Where long drawn or ground bars of a standard size carry many parts, e.g. line shafting, textile and agricultural machines | #### Why hole basis is preferred - Holes are made by drills, reamers, boring and broaches whose sizes are fixed; one reamer size of H7 covers all fits. - Shafts are easily turned and ground to any size, so the changing member is the cheaper one to change. - Fewer tools and gauges are needed, so the cost of production and inspection is lower. The shaft basis is used when a single shaft carries several parts with different fits (for example a bar on which several bearings, collars, and pulleys are fitted) because cutting steps on a shaft would weaken it and cost more. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the hole basis system, which statement is correct? A. The hole has zero lower deviation (H) and the shaft size is varied B. The shaft has zero upper deviation (h) and the hole is varied C. Both hole and shaft deviations are zero D. The hole has zero upper deviation and the shaft is fixed Answer: A. Hole basis fixes the hole at the basic size as its minimum limit and varies the shaft. (Key point: Fixed member) 2. Why is the hole basis system more commonly used? A. Shafts need special reamers for each size B. Holes are made by fixed-size tools (reamers, broaches), while shafts can be turned or ground to any size easily C. Holes are easier to grind to any size than shafts D. It gives tighter fits than the shaft basis Answer: B. One standard reamer or gauge size covers all fits, so changing the shaft is the cheaper option and fewer tools are needed. (Key point: Why hole basis preferred) 3. When is the shaft basis system preferred? A. For general machine tool work B. When only drills and reamers are available C. When one long drawn or ground bar carries several parts with different fits D. When the highest interchangeability of tools is wanted Answer: C. Cutting steps on a standard bar would weaken it and cost more, so the bar is kept at standard size and the holes are varied. (Key point: Shaft basis use) 4. In the shaft basis system, the basic size is which limit, and what letter denotes the shaft? A. Minimum limit of the shaft; H B. Maximum limit of the hole; h C. Minimum limit of the hole; H D. Maximum limit of the shaft; h Answer: D. In shaft basis the upper deviation of the shaft is zero (h) and fits are obtained by varying the hole. 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