This is the one piece sub-chassis for the Linn Sondek LP12 SME tonearm.

Why one piece? Your high-end cartridge tip is in microcontact sufrace area with your vinyl track.

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.