Propeller Shaft Anodes — Streamlined Collar

Propeller Shaft Anodes — Streamlined Collar

Two-piece streamlined collar anodes that clamp directly to the propeller shaft, in 31 sizes from 1/2 in to 6 in and 25 mm to 60 mm. Available in zinc, aluminium or magnesium — tell us the water and we will quote the right alloy.

Imperial shafts

Shaft diameter	Equivalent	Typical weight	Common reference
1/2 in	12.7 mm	0.23 kg (0.51 lb)	CMX00
3/4 in	19.05 mm	0.38 kg (0.84 lb)	CMX01
7/8 in	22.23 mm	0.43 kg (0.95 lb)	CMX02
1 in	25.4 mm	0.45 kg (0.99 lb)	CMX03
1-1/8 in	28.58 mm	0.52 kg (1.15 lb)	CMX04
1-1/4 in	31.75 mm	0.53 kg (1.17 lb)	CMX05
1-1/4 in (extra heavy)	31.75 mm	0.79 kg (1.74 lb)	CMX05A
1-3/8 in	34.93 mm	0.67 kg (1.48 lb)	CMX06
1-1/2 in	38.1 mm	0.76 kg (1.68 lb)	CMX07
1-3/4 in	44.45 mm	1.13 kg (2.49 lb)	CMX08
2 in	50.8 mm	1.41 kg (3.11 lb)	CMX09
2-1/4 in	57.15 mm	2.76 kg (6.08 lb)	CMX10
2-1/2 in	63.5 mm	2.35 kg (5.18 lb)	CMX11
2-3/4 in	69.85 mm	3.42 kg (7.54 lb)	CMX12
3 in	76.2 mm	2.97 kg (6.55 lb)	CMX13
3-1/4 in	82.55 mm	3.27 kg (7.21 lb)	CMX14Z
3-1/2 in	88.9 mm	4.10 kg (9.04 lb)	CMX15
4 in	101.6 mm	4.04 kg (8.91 lb)	CMX17
4-1/2 in	114.3 mm	5.63 kg (12.41 lb)	CMX18
5 in	127 mm	4.20 kg (9.26 lb)	CMX19
5-1/2 in	139.7 mm	7.24 kg (15.96 lb)	CMX20
6 in	152.4 mm	5.44 kg (11.99 lb)	CMX21

Metric shafts

Shaft diameter	Equivalent	Typical weight	Common reference
25 mm	0.984 in	0.549 kg (1.21 lb)	CMX25
28 mm	1.102 in	0.581 kg (1.28 lb)	CMX28Z
30 mm	1.181 in	0.558 kg (1.23 lb)	CMX30
35 mm	1.378 in	0.730 kg (1.61 lb)	CMX35
40 mm	1.575 in	1.429 kg (3.15 lb)	CMX40
45 mm	1.772 in	1.261 kg (2.78 lb)	CMX45
50 mm	1.969 in	1.075 kg (2.37 lb)	CMX50
55 mm	2.165 in	2.735 kg (6.03 lb)	CMX55
60 mm	2.362 in	2.672 kg (5.89 lb)	CMX60

The anode is sized by the shaft it clamps to, so each size is listed in the shaft's own unit with the equivalent alongside. Measure the shaft, do not measure the old anode — a half-wasted anode reads undersize. Weights are typical for the streamlined profile and are confirmed at quotation.

Got an old part number?

The reference column above is the number most commonly cast into this style of anode. If the number on the one you removed is not there, send us a photo of it and the shaft diameter and we will match it — most aftermarket numbering descends from the same US military specification, so nearly everything cross-references.

Which alloy

Zinc	Salt water. To ASTM B418 Type I — the alloyed seawater grade, whose composition also meets MIL-A-18001K.
Aluminium	Salt and brackish water. Al-Zn-In alloy; longer life per kilogram and now the default on new offshore work.
Magnesium	Fresh water only, to ASTM B843. Never use it as a saltwater substitute — it wastes in months.

For fresh water and buried service in zinc, ASTM B418 Type II is the high-purity grade. Tell us the water and we will quote the right alloy rather than assume.

Sizing

The material specs say nothing about how much anode to fit. That comes from ABYC E-2 for boats and DNV-RP-B401 for ships and offshore structures, which size the anode mass against the area to be protected, the current density and the design life.

Whatever the calculation says, the maintenance rule is the same: replace at about 50% wasted. A half-wasted anode is not a half-working anode — output falls away as surface area is lost, so the last half protects far less than the first.

What to put on your purchase order

Zinc anodes fail by passivating — they skin over and stop producing current while still looking perfectly serviceable on the shaft. The usual cause is iron contamination, which is exactly what ASTM B418 caps at 0.005%. Specify "to ASTM B418 Type I, mill certificate with each lot" and you have something to test against. Without it, a cheap anode that does nothing looks identical to a good one until the shaft is pitted.

See the anode selection guide for the full alloy, sizing and specification detail.