Wall Street's top regulator on Wednesday unveiled rules allowing stock markets to price shares in increments of half a penny, rather than the current minimum size of 1 cent, aiming to promote more competitive pricing and reduce investor costs.

The price increments at which thousands of stocks and ETFs are quoted look set for an overhaul Wednesday, when the US Securities and Exchange Commission votes on final rules to reduce them to less than 1 cent.

The proposals being considered by the Securities and Exchange Commission are tamer versions of the ambitious revamp of stock trading that Chair Gary Gensler proposed two years ago.