Jolandi -- I would probably not use the center top bolt, if the mold were mine. As you pour the soap batter into the mold, the bolt will get covered in batter and be hard to clean. If you want to do any decorative work in or on the soap, the bolt will get in the way of your work. Also, the pressure of the soap batter is not very high for a mold that short and sturdy, so a center fastener is really not adding a lot. You have a bolt in the center of the bottom, and that should be more than enough. Just something to think about...
To all -- When designing a mold, keep in mind that your soap bars will shrink in height, width, and length as they cure. If you want to shoot for a specific bar size, be sure to add a little extra to your mold dimensions to allow for shrinkage of the cut bars. My rough rule of thumb is about 1/8 inch (3 mm) of shrinkage in the two longer dimensions of a soap bar and "a smidge" (maybe 1 mm) in the shortest dimension.
To all -- When designing a mold, keep in mind that your soap bars will shrink in height, width, and length as they cure. If you want to shoot for a specific bar size, be sure to add a little extra to your mold dimensions to allow for shrinkage of the cut bars. My rough rule of thumb is about 1/8 inch (3 mm) of shrinkage in the two longer dimensions of a soap bar and "a smidge" (maybe 1 mm) in the shortest dimension.
