1.08 by 1.08 inches square as per instructions, with baille;
Sanskrit numerals form the magic square associated with the holy planet Jupiter and the holy number three.
There are yantras for the Sun (http://shpws.me/LiNs), Moon (http://shpws.me/LiMv), and Venus (http://shpws.me/LiND) as well. All other grahas ("planets" in Jyotish or Vedic astrology) are also available by request (/contact.html).
These are available in many varieties of silver and gold, including very inexpensive plated versions.
For more information, see the book Numerology by Harish Johari (http://www.amazon.com/Numerology-Ayurveda-Astrology-Harish-Johari/dp/0892812583/). Here (https://en.wikipedia.org/wiki/Magic_square), here (http://hans.wyrdweb.eu/tag/magic-square/), and here (http://www.magicalrecipesonline.com/2012/07/venus-in-vedic-astrology-and-lord-sukra.html)are some more sites worth reading.