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No worries. You cant fit a heatsink and fan inside these cases. If you want a heatsink, a fan needs to be mounted on the outside of the case. You can only fit the 25mm x 25mm x 10mm heatsink inside the 30mm fan case if you're mounting a fan outside.. On the 40mm fan case, you could use up to a 25mm x 25mm x 15mm heatsink, as long as you position it correctly so it doesnt hit into the nuts on the underside of the fan.