Today in 1909, US Patent 914787 A was issued, an invention of James W. Brainard, for his “Wooden Barrel or Keg and Head Therefor.” There’s no Abstract, but the first paragraph tells the tale, sort of (the OCR didn’t do the best job and I had to do a fair bit of guessing):

The prime object of the present invention is to equip an ordinary barrel or keg made up of wooden staves, with an improved head which detachably held in plate in a simple and effective manner, without the employment of extraneous fastening means, and is arranged to stiffen and strengthen the barrel without detracting from any of its essential features. It is proposed to form the head from single blank of sheet metal, and to shape the some so as to permit of the convenient application and removal thereof without making the barrel material change or alteration in in this connection, the head is arranged rel. to embrace the chime of the barrel or keg so as to incase the same in a metal shield, which rotc’cts the extremities of the staves when in and on the barrel or keg, particularly when rolling the same.