The Heavy Duty Manifolds are designed to allow high flow rates. The manifolds are available in 2 way or 4 way.
The 3/4" inlet connects to your air pump or compressor. The multiple 5/8" outlets will connect to 5/8" air hose delivering air to your diffusers. The fittings are high quality brass. Size the manifold to your air pumps air output.
HK25L through HK80L air flow can handle 2 way or 4 way manifolds.
HK100L and HK120L should use the 4 way only so as not to restrict air flow.
NOTE !! The outlet fitting of the HK25L through HK100L is a 5/8" diameter. You can connect the 5/8" pump outlet directly to the 3/4" manifold inlet with a short piece of 5/8" or 3/4" hose ( supplied with air pump). However, the 2 way or 4 way manifold outlets are only 3/8" so you must reduce down to 3/8" hose to feed your air diffusers. The HK120L outlet fitting is 1". You will need a reducer hose from 1" to 3/4" (supplied with HK120L) in order to connect the HK120L to the manifold inlet. And then use 3/8" hose to feed your air diffusers.
The 1/2 HP and 3/4HP rocking Piston Compressors should use the 4 way manifold.