Dometic Marine (formerly SeaStar Solutions and Teleflex Marine) makes several different models of hydraulic steering. Here is a breakdown on them and their key features:

BayStar
The BayStar is Dometic's most economical hydraulic kit, which is good up to 150 hp and 50 mph, for single outboard and single helm. Not suitable for high-performance, pontoon, sterndrive, inboard, or bass boats. The most common BayStar kit is HK4300-4, which contains an HH4314-4 helm, HC4645-3 cylinder, HA5430H fluid (2 qts), filler kit, and instructions. A SeaStar hose kit must be purchased in the desired length.

Verify the specific cylinder your outboard requires by viewing the cylinder application guide image for BayStar on the kit pages.

The BayStar can be configured with a tilt helm, which is helm part number HH4315-3.

SeaStar
The SeaStar is Dometic's most popular hydraulic kit, and is suitable for a wide range of boats. It can handle up to 350 hp and 60 mph. There are many configurations and options, and it can be used with outboards, sterndrives, and inboards, as well as multi-helm and multi-engine setups. If you have a 60mph+ boat or bass boat, the SeaStar Pro is recommend (see next section).

The most popular SeaStar kit for a single outboard and helm is HK6400-4, which contains an HH5271-4 helm, HC5345-3 cylinder, HA5430H fluid (2 qts), filler kit, and instructions. A SeaStar hose kit must be purchased in the desired length. The SeaStar hose part number starts with HO51 and the last two digits are the length in feet (e.g.: HO5118 is an 18ft hose kit).

Verify the specific cylinder your outboard requires by viewing the cylinder application guide image for SeaStar on the kit pages.

SeaStar Pro
The SeaStar Pro is made by Dometic specifically for high-performance, 60mph+, and bass boats. The standard kit is HK7500-4, which contains an HH5770-4 helm, HC6345-3 cylinder, HA5430H fluid (2 qts), filler kit, and instructions. Just like the SeaStar, it does not include hoses as they come in pre-made lengths. The SeaStar Pro hose kits start with HO57 (and not HO51) since they are Kevlar-reinforced to handle higher loads than the standard SeaStar hoses.

Filler Kit
The HA5438 filler kit is included in all regular kits. If buying components individually, it will be inside the cylinder box. Generally, there's no need to purchase it individually, unless you're reusing an existing cylinder.

Optimum Performance Chart for Outboard Engines