Jim
You're better off without a strainer over the through hull as they can clog easily and there is no way to clear them while in the water. A better idea is to install one of these inside to strain out debris.
West Marine: Raw Water Strainer Product Display 710&Ne=0&Ntt=strainers&Ntk=Primary Search&Ntx=mode matchallpartial&Nao=0&Ns=0&keyword=strainers&isLTokenURL=true&storeNum=11&subdeptNum=70&classNum=71
But there are better prices than West. Check Jamestown oe Defender.