Seems like an Extreme Heavy Duty amplifier holder to hold the chassis in place during assembly but to allow rotation to access various sides.

If it's a rotisserie, I want one.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8