The thickness of a bowtie inlay can vary depending on several factors such as the size and type of wood being used along with the purpose of the joint itself. In general, however, it is recommended that the thickness be roughly one-third (1/3) of the total thickness of the wood being joined together. This ratio ensures that both pieces retain sufficient strength while also allowing for proper adhesion and support from glue or other bonding agents used during installation. It's important not to make the inlay too thin, as this could compromise its effectiveness as a reinforcing element. Additionally, a thicker bowtie inlay may be needed for larger and more heavy-duty applications where additional strength and stability are required. Ultimately, the thickness should be chosen based on the specific project requirements and the desired visual aesthetics.