I just bought a 55 gal. aquarium at a garage sale and it doesn't have any center bracing. It was manufactured in 1979 acording to the date sticker. It's not broke or missing or anything, it just wasn't made with one. The glass thickness is 3/8 inch and was just wondering if it just has thicker glass and that's why.....My 40 gal tank has 1/4 inch thick glass with bracing.