S-adenosyl-L-methionine-dependent methyltransferase responsible for the addition of the methyl group in the formation of N6-methyl-N6-threonylcarbamoyladenosine at position 37 (m(6)t(6)A37) of the tRNA anticodon loop of tRNA(Thr)(GGU). The methyl group of m(6)t(6)A37 appears to slightly improve the efficiency of the tRNA decoding ability. Binds to tRNA. N(6)-L-threonylcarbamoyladenosine(37) in tRNA + S-adenosyl-L-methionine = H(+) + N(6)-methyl,N(6)-L-threonylcarbamoyladenosine(37) in tRNA + S-adenosyl-L-homocysteine Homodimer. Belongs to the tRNA methyltransferase O family.