I use 7/8 oz Hermann Oak for unlined Banjo Straps, the back side isn’t dyed. I use Fiebings Aussie leather conditioner on both sides, that gives the backside that darker look and to keep dye from rubbing off . The Aussie makes the leather of the banjo strap very supple when you apply to front and back, heat with a heat gun (or hair dryer), then remove the excess by buffing. I seal the top side with Clear Lac. Putting the Aussie on both sides also helps with perspiration resistance which is another great benefit on an instrument strap.