Knuckle Arm
The "Knuckle arm" (steering arm) is sandwiched between the Ball Joint and the Strut assembly.
Overview
Knuckle arm also known as "steering arm". It turns the strut to which the front wheel is bolted, thus steering the vehicle. The arm is pushed/pulled by the tie-rod of the Steering Linkage.
Steering arm. The threaded bolt is to adjust the steering angle stop
Knuckle arm bolts to the bottom of the Strut
Special shoulder bolt required to take up shear load
Datsun knuckle arms come in two basic sizes, 75mm & 80mm:
- 75mm narrow bolt spacing for 45mm strut tubes (used by B110)
- 80mm wide bolt spacing for 50.8 mm strut tubes (used by most other Datsuns including 280ZX)
- 91mm spacing on 240Z
There is only one size for 1200, to fit 45mm strut type. But it comes in two versions: 1970-1975, and 1976-up.
H10 balljoint (small taper) * for small-bolt-pattern LCA (B110, early 120Y)
H74 balljoint (large taper) * fits large-bolt-pattern LCA (late 120Y/B120/B310)
casting marks identify
H74
Bolted to the balljoints
W50
Quick Ratio Arm
Consider the length of the arm: long arm gives a slower steering response, but less effort is required to turn the wheels. Shorter arms give faster response.
Change the length of the steering arm without changing the steering idle arm length will impact the front suspension bump steer characteristics.
Unfortunately the large-size B310 arm (commonly used when swapping struts) will change your 15:1 steering to an effective 16:1 as the arm is 7% longer. Even worse, when putting 2" struts in a 45mm B310 vehicle, the stock B310 16.4:1 steering will effectively turn into a slow 17.6:1.
Short-arm Modified for use with 2" struts
Pitroad sells modified quick steering arms.
Comparison
It seems B310 with W5000/W5060 steering arm uses the same size tie-rod ends as the smaller units (B110 and B210).
* B310 small: rounded 
* B310 large: knobbed area around the ball joint hole 
Knuckle Arm
B120 early +H1000/H1025 rod assy H1000/H5000
B120 7510- +H1025 rod assy H7400 -8507 H7440 8508-
H7440
B210 early +H5025 H5000 H7400 late van
B210 late +H5025 rod assy H7400
PB210/USA B210 +H5800 rod assy U0101
B310 +W5025 rod assy H7400 regular cars
H74
W5000/W5060 power cars
B310 Steering Knuckle Arms
B310
Part Numbers
See also: Front Axle Part Numbers
See also: Steering Linkage Part Numbers
steering arm 40052 = Knuckle Arm RH 40053 = Knuckle Arm LH
Knuckle Arm RH B10: 40052-18000ᴳ (different from newer models) B110: 40052-H1000ᴳ < 40052-H5000ᴳ PB110: 40052-H2501ᴳ 510: 40052-H2501ᴳ from 1972 510 > 40052-H2500ᴳ > 40052-A8600ᴳ B120: 40052-H5000ᴳ to 1974 B120: 40052-H7400ᴳ 7510- <> 40052-H7440ᴳ B210: 40052-H5000ᴳ (74-75 A12) B210: 40052-H7400ᴳ (1976-up A engine, except USA) B210: 40052-U0101ᴳ (USA, also PB, also L16) B310: 40052-W5000ᴳ (All US, all A15, most A14) <> 40052-W5060 B310: 40052-H7400ᴳ (A12, A13, and budget A14 models) A10: 40052-W5000ᴳ ALL <> 40052-W5060ᴳ
Knuckle arms bolted to ball joints
W50
* 1977-1981 A10 Stanza/510 * 1978-1982 B310 fitted with 13" wheels
B310
CANADA B310 H74 - A12A cars W50 - A14/A15
JAPAN B310 
40052-H7400ᴳ ARM-KNUCKLE RH ALL round headlight except GX#,Wagon S,K.A12A/A13 square headlight Van 40052-W5000ᴳ <> 40052-W5060ᴳ GX# round headlight (OPTION) S,K.A14/A15 square headlight Wagon USA B310 W50 - all [including A12A-powered cars]
Compare W50 arm use with the 13" wheel fitment WHEEL ASS'Y-ROAD B310 JAPAN 12 x 4J GRAY 12 x 4J SILVER 13 x 4.5J SILVER 40300-W8300ᴳ S,K,W square headlight S/# 40300-W5700ᴳ GX# round headlight W.GL round headlight 40300-U7400ᴳ W.DX round headlight 13 x 5 alloy Type B 40300-U7527ᴳ/40300-U7528ᴳ (W/KEY) OPTION for W OPTION for GX round headlight OPTION for S,K.A14/A15 13 x 5 alloy Type C 40300-W6027ᴳ/40300-W6028ᴳ (W/KEY)
Bolts
See also: Front Axle Part Numbers
40055-H1000ᴳ BOLT-KNUCKLE ARM 44mm 08911-64010 NUT-HEX M10x1.25 High, medium carbon steel (2 each side) 08915-14010 WASHER-SPRING lock medium M10 (2 per side)
The 44mm bolt replaced the earlier 38mm long version which was used on one side. After 1973 February the long bolt was used on each side.
Spacers
When Lowering the front suspension, if going ultra-low, strut spacers (roll center adapters) are used. They are intended to correct the lower arm angle when the vehicle height is dropped to address the change in front roll instant center.
Main: Roll Center Adjusters
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