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32.5" Dark Bronze Anodized Aluminum Adjustable Oak Top Sill Residential Threshold
I would not recommend merely caulking the threshold down. Unfortunately there is no concealed location on this threshold to pierce through in order to drive a mechanical fastener. I recommend that you drill through the aluminum portion large enough so as to sink a mechanical fastener through the wood substrate - look for pressing caps to close off the hole that you've drilled in the aluminum. I would certainly set all of this into a bed of exterior rated caulk as well and even further I would completely seal all sides of the wood substrate so as to help resist a long-term fatigue and failure of that wooden structure which I believe is simply a softwood species of lumber such as pine.