In Japan, there are many types of mirror (The top of a maru-dai. Maru means round.) because every artisan makes their own marudai themselves. My favorite type of maru-dai has a mirror with a gentle slope starting at the middle of the radius down to the center hole.
Sizes of marudai: The top of the marudai (we call it mirror) is 25-30 cm in diameter (or square or octagon). The center hole is 3-4 cm in diameter. The height is 40-45 cm (when you use the marudai kneeling down) or 60-65 cm (when you use marudai sitting on a chair), it depends on your size.
Kakudai (Square top. Kaku means square) has been used for braiding upwards. The bobbins are spun so that the thread is twisted, giving a special effect. Four straight ends are useful to prevent four groups of threads from mixing with the neighbor group because the upward tension makes the position of a thread at the mirror edge less stable than that on maru-dai.
Total weight of weight bobbins is 2 to 2.5 times larger than that of the center weight. In Japan most people use heavy weight bobbins to make OBIJIME. But it is not necessary to use such heavy weight bobbins to make ordinary braids. For example:
8 bobbins (240 g of each) need 600 to 800 g of center weight.
16 bobbins (100g of each) need 550 to 700 g of center weight.
If you want to have a marudai instantly