This is a modern style, standard banjo bracket nut wrench fitting 9/32" (about 7.14mm) nuts. It's very well made with correct proportions, precisely machined socket and good plating.
Other than for Goodtime banjos as advertised, this T-wrench fits nicely most vintage Asian banjos up to early 1990's as well as a few recent instruments and some old ones, mostly open back reproductions equipped with vintage style closed nuts. This wrench is sort of middle size between Gibson size (1/4", 6.35mm), the most widespread bracket nut size among either American or Asian banjos, and 5/16" (7.93mm), both unavailable from Thomann at the time of this writing.
With the notable exception of Recording King (assembled in the USA thus sporting SAE sized threads), nearly all the Asian banjos on the market these days are equipped either with 18 to 24 flat hooks for entry level wood rimmed models, 24 round hooks (far more rugged and by the way stock on both Harley Benton BJ-55Pro and BJ-65Pro, Thomann's house brand) for the better models with either shoes, tube&plate or one piece flange, and 30 flat hooks for the so-caled 'bottlecap' banjos built around an aluminium integral rim/ring/flange. The bracket nuts for nearly all of the above are smaller (1/4") and require a Gibson size key which unfortunately is not standard supply as it should since very few makers do supply one along with the banjo. Most American online stores and warehouses sell it though.
Since many about the better Asian banjos including the costlier ones come randomly from the factory with an Allen trussrod wrench often accompanied by the unwieldy L-shaped combination bracket wrench/Phillips screwdriver instead of the proper (and traditional) bracket T-wrench, I can but recommend purchasing one of these excellent Deering T-wrenches if your banjo is equipped with 9/32" nuts, more than one to have another handy at home if you own more than one banjo with the same nut size. Moreover, this little tool is an absolute must if you happen to work on banjos.