The Rudder and hardware are the same in both of these assemblies.
The length of the mounting bracket is the only difference.

• Item#: SPDR-005-M MONO Mini Rudder assembly, as pictured
• Item#: SPDR-005-H HYDRO Mini Rudder assembly, as pictured
  Price: $39.95

• Item#: SPDR-006 Mini-Rudder blade only.
  Price: $18.00

• Item#: SPDR-007 Mini Rudder Blade & Bearing Block Assembly
  Price: $33.00

There are no pictures available for the items listed below

• Item#: SPDR-003-M MONO Mini Rudder Transom Bracket ONLY
• Item#: SPDR-003-H HYDRO Mini Rudder Transom Bracket ONLY
• Item#: SPDR-008 Mini-Rudder Control Horn ONLY
  Price: $5.60
  
  
• Item#: SPDR-009 Teflon Rudder Bushing for Mini-Rudder's and .21
  Price: $1.36