Here is the bearing sizes and there are a lot better bearings out there then the stock STS bearing.
Front Bearing #607 (7mm X 19mm X 6mm)
.21-.30 Main Bearing #2514 (14mm X 25mm X 6mm)

Here is STS manufacturers web site.
http://www.stsrc.com.tw/

I use to be sponsored by a company that use to sell STS engines in the US. He closed his business. In the last 8 months have been running large scale and still have 4 STS engines. One D21B new in the box. I think the STS D21B is the best budget engine out there. VERY STRONG! If I can help let me know.