This is the one piece sub-chassis for the Linn Sondek LP12 in case you have one Naim ARO tonearm.
Why one piece?
In case of two pieces, there is discrepancy between arm board and sub-chassis, they are not flat.
Once piece arm board and sub-chassis is machined to 0.05 mm error in flatness bewteen Tonearm and Platter.
In addition, both arm board and sub-chassis are the same material.
This very a thick sub-chassis compares with your origianl sub-chassis.
It is custom made to the weight at 960g, and therefore it is much easier to adjust the springs bouncing for better performance in case you have a heavy.
No need to talk more, you know the improvement in sound by upgrade to one piece arm board and the sub-chassis.