Change font size programmatically on thermal Bluetooth Printer

let hexs = [0x1b,0x21,0x20] //doubleWide
var hexString = String() 
for all in hexs {
    if let scalar = UnicodeScalar(all) {
        hexString.append(Character(scalar))
    }
}
let theData = hexString.data(using: .utf8)!
myPrinter.writeValue(theData, for: printCharacteristic, type: .withoutResponse)

//printCharacteristic corresponds with Service/Characteristic B

[0x1b,0x21,0x00] //default
[0x1b,0x21,0x01] //small font
[0x1b,0x21,0x08] //bold
[0x1b,0x21,0x10] //doubleHeight
[0x1b,0x21,0x20] //doubleWidth
[0x1b,0x21,0x20] //doubleHeightAndWidth