headlight bulbs H1 H4 H11 bulb You would assume that buying headlight bulbs is a no-brainer, but that’s not true. The different types of bulbs (like H4, H7, and H11) and the many choices (brands, bulb groups, power source, and designs) out there will no doubt overwhelm the uninitiated.
Once the class of thread and part tolerance has been defined, an H limit is selected to produce a thread that is within the minimum and maximum limits for that class if fit. These limits are the same as the Go and Not Go thread plug gage dimensions. The goal is to select a tap with an H-limit that is near the middle of the part tolerance. .