Contributes to the release of free fatty acids from fatty acid synthase (FASN). Has broad substrate specificity, giving rise to a range of free fatty acids with chain lengths between 10 and 16 carbon atoms (C10 - C16). (9Z)-octadecenoyl-[ACP] + H2O = (9Z)-octadecenoate + H(+) + holo-[ACP] decanoyl-CoA + H2O = CoA + decanoate + H(+) dodecanoyl-CoA + H2O = CoA + dodecanoate + H(+) H2O + tetradecanoyl-CoA = CoA + H(+) + tetradecanoate H2O + hexadecanoyl-CoA = CoA + H(+) + hexadecanoate Interacts (via C-terminus) with FASN. Detected both in lactating and non-lactating breast epithelium (at protein level) (PubMed:6589427). Isoform 2 is up-regulated in bone marrow-derived mononuclear cells of rheumatoid arthritis patients (PubMed:17082220). Belongs to the thioesterase family.