Sigma 70mm 2.8 macro

OK. I've had my sigma 70mm for a while now and have had no luck finding a lens cap that will work with the SCREW on hood attached to the lens. I like leaving the hood on all the time but the stock lens cap will not work with the hood on and I hate to have to screw the hood on every time I use the lens. I know they make cloth ones that kind of tie on but this is not what I want. I'd like a slip on cap or even a snap in if possible. Anyone?
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Roy Martin