it takes 2 bearings in each brake arm, 19mmx10mmx5mm. these are quite cheap and easy to get hold of. i'm sure the axle is from a sealed 10mm rear hub cut to length. you will need small spacers in between the bearings on the brake arms about 3mm wide. the part to hold the spring will probably need to be homemade. i dont know if the brake arms were milled out to suit the bearings but i assume they were, you would need to check the size once you've stripped a brake down. i'll strip down my rob ridge boa and get some pics.