The U.S. manufacturing sector expanded in September but at a slightly slower rate than in August, according to the Institute for Supply Management's key purchasing managers' index for manufacturing released today. August's reading of expansion was the first after 18 months of contraction.

September's index reading was 52.6, down from 52.9 in August. Readings of more than 50 indicate expansion.

The employment portion of the index, however, contracted at a quicker rate in September (with a reading of 46.2) than in August (46.4).