Tungsten disc can add additional weight to your hammer.

106mm 3kg to 4.75kg can achieve 5kg and 5.25kg with 1 additional Tungsten disc

120.5mm 5.25kg to 7.25kg can achieve 7.5kg and 7.75kg with 1 additional Tungsten disc and 8.25kg with 2 tungsten discs.

128mm 6.5kg to 8.5kg can achieve 8.75kg and 9kg with 1 additional Tungsten disc and 9.5kg with 2 tungsten discs.