Which brass component should not be cleaned up in advance before inletting?

When preparing for inletting, it is essential to ensure that components fit precisely within the wood. The rear thimble, or component C, typically should not be cleaned before inletting because doing so may remove critical material that serves to achieve a tight fit. This specific area often requires a precise and tailored interaction with the wood to ensure stability and strength in the final assembly.

Cleaning up the rear thimble in advance could potentially alter its dimensions and therefore disrupt the fit of the component within the stock. The rear thimble often needs to be inletted for a secure fit, and any pre-cleaning might compromise the necessary adjustments during that process.

In contrast, other components like the front thimble, middle thimble, and bottom thimble can often be cleaned in advance since they might not require such intricate fitting adjustments as the rear thimble. This makes it clear why leaving the rear thimble as is until after the inletting process is the preferred approach.