For non-US residents, with a completed US Tax Form (W8-BEN etc) the withholding tax is 15%. We arrange to have this form completed and lodged on your behalf by our US broker partner. 

However, without completing and lodging the US Tax Form (W8-BEN etc) the withholding is 30%.

This withholding amount is only on dividends paid and not on share sales. 

Please note that due to the complexities involved with tax, please obtain independent & professional advice which takes into account your own set of facts and circumstances.