The U Brackets used in these plans are supplied by Tasman Engineering (NZ) but most trailer parts suppliers will have similar sized brackets available depending on the rollers available.
U Bracket 3017 is used for all wobble roller pivots, both dual and quad, and can be fixed directly to the chassis if the correct mounting position is known. For a fully adjustable trailer, weld these to 40 x 40 x 3.0 SHS stems and U bolt to the chassis.
U Bracket 2887 is for mounting MK3 rollers (NZ) (79mm long roller with 40mm diameter core, 60mm diameter flanges and 16mm bore).
Where MK3 rollers are unavailable, use a 3" (75mm) bow or cotton reel roller and the corresponding U bracket.
The largest roller used in these plans is the MK10 (NZ) (136mm long roller with a 60mm diameter core, 91mm diameter flanges and 16mm bore)
Again, if this roller is unavailable in your area/country, a 5" or 6" (125 - 150mm) self centering or cotton reel roller with the corresponding U bracket should be used.
Good quality keel rollers will have replaceable nylon/high impact plastic bushings on the inner bore. Due to the high loads these rollers are normally under, rollers without bushes will fail quickly and become a hindrance to launching and retrieving your boat.
Always use stainless steel pins, split pins and either galvanised or stainless steel washers.