We examine experimentally and theoretically the effect of polymer adsorption layers on the stability of metal nanoclusters. We find that, somewhat contrary to expectation in this low volume fraction limit, the thickness of the adsorbed layer does not increase linearly with the number of repeating units in the chain (i.e., molecular weight), N. Rather, in the range we examine experimentally it decreases with molecular weight, in agreement with our model predictions. The number of contacts between the polymer chain and the cluster surface, i.e., polymer anchoring points, increases significantly with N, as does the polymer volume fraction in the adsorbed layer. As a result, although a large fraction of active surface sites remains available, particles stabilized by long chains resist flocculation, while particles stabilized by short chains do not.