A reference table correlating tap sizes to the appropriately sized drill bit needed to create a pilot hole for threading operations. The chart indicates the correct drill bit size to use based on the desired thread size and pitch, ensuring sufficient material remains for the tap to create clean, strong threads. For example, if a project requires a 1/4-20 thread, the reference material would specify the drill bit diameter necessary to pre-drill the hole.
Accurate pilot hole sizing is crucial for successful thread creation and the longevity of threaded connections. Undersized holes can cause tap breakage and make threading difficult, while oversized holes weaken the threads and reduce holding power. Historically, machinists relied on printed versions of these guides to quickly determine the correct drill size in a shop environment, facilitating efficient and accurate work. This practice ensures properly tapped holes and reduces material waste.
The following sections will delve into the considerations for material selection, the impact of different thread standards, and online resources for accessing this information digitally, allowing for informed decisions regarding threading operations.
