The thickness of a tsuba, the handguard on a Japanese sword, can vary depending on the design, style, and purpose of the sword. There is no standard or fixed measurement for tsuba thickness, as it can be influenced by personal preference, historical period, and the type of sword it is intended for.

Generally, tsuba thickness falls within a range of 3 to 8 millimeters (0.12 to 0.31 inches). Thinner tsuba are typically found on lighter swords like wakizashi or tanto, while thicker tsuba are often seen on larger swords such as katana.

The primary function of a tsuba is to protect the hand of the swordsman during combat, deflecting and blocking strikes from the opponent's weapon. As such, tsuba thickness should provide sufficient structural strength to withstand impact and effectively serve its protective purpose.

It's worth noting that tsuba thickness is just one aspect of its design, and other factors like shape, size, and material composition also contribute to its overall effectiveness and aesthetic appeal. If you have a specific sword or style in mind, it's advisable to consult with a knowledgeable swordsmith, collector, or practitioner who can offer guidance tailored to your particular needs and interests.