机车轴式
Clash Royale CLAN TAG#URR8PPP 
以華氏式別分類的蒸氣機車
1900年代的华氏式别手册。[1]
在铁路技术上，机车轴式，或称机车轮式，是指用英文字母和阿拉伯数字的组合来表达铁路机车走行部车轴排列结构和特点的系统化分类方式。世界上各地使用的机车轴式表达系统主要有三种。
华氏轮式：这是最早出现的机车轴式分类系统之一，广泛应用于蒸汽机车的识别，主要为美国、加拿大、英国、爱尔兰等地采用。
AAR轴式：是一种由美国铁路协会所制定的轴式分类法，主要应用于美国和加拿大的柴油机车和电力机车。
UIC分类法：是一种由國際鐵路聯盟制定的轴式分类法，广泛应用于欧洲和亚洲国家。
不同机车轴式之對比
UIC軸式
VDEV/VMEV/UIC-System
華氏式別
（Whyte-Notation）美式稱呼 簡單圖解
左方為機車前進方向A1
0-2-2Oo A2
0-2-4Ooo 1A
2-2-0Planet oO 1A1
2-2-2Patentee oOo 1A2
2-2-4oOoo 2′A
4-2-0Crampton, Norris, Jervis ooO 2′A1
4-2-2Single Driver ooOo 2A2
4-2-4ooOoo 3A
6-2-0Crampton oooO N/A
0-3-0OOO B
0-4-0Four-Wheel-Switcher OO B1
0-4-2OOo B2′
0-4-4Forney OOoo B3′
0-4-6OOooo 1B
2-4-0Hanscom oOO 1′B1′
2-4-2Columbia oOOo 1B2′
2-4-4oOOoo 1B3′
2-4-6oOOooo 2′B
4-4-0American, Eight-Wheeler ooOO 2′B1′
4-4-2Atlantic ooOOo 2′B2′
4-4-4Jubilee ooOOoo 2′B3′
4-4-6ooOOooo C
0-6-0Six-Wheel-Switcher OOO C1
0-6-2OOOo C2′
0-6-4OOOoo 1′C
2-6-0Mogul oOOO 1′C1′
2-6-2Prairie oOOOo 1′C2′
2-6-4Adriatic oOOOoo 1′C3′
2-6-6oOOOooo 2′C
4-6-0Ten-Wheeler ooOOO 2′C1′
4-6-2Pacific ooOOOo 2′C2′
4-6-4Hudson, Baltic ooOOOoo D
0-8-0Eight-Wheel-Switcher OOOO D1
0-8-2OOOOo D2′
0-8-4OOOOoo D3′
0-8-6OOOOooo 1′D
2-8-0Consolidation oOOOO 1′D1′
2-8-2Mikado oOOOOo 1′D1′
2-8-2TMacArthur oOOOOo (1′D1′)(1′D1′)
2-8-2+2-8-2Double Mikado, Garrett oOOOOo+oOOOOo 1′D2′
2-8-4Berkshire oOOOOoo 1′D3′
2-8-6oOOOOooo 2′D
4-8-0Twelve-Wheeler, Mastodon ooOOOO 2′D1′
4-8-2Mountain, Mohawk (NYC) ooOOOOo 2′D2′
4-8-4Northern, General Service (SP), Golden State (SP), Niagara (NYC), Wyoming ooOOOOoo 2D3
4-8-6ooOOOOooo 3′D3′
6-8-6
nameless (Pennsylvania Railroad Steam Turbine)oooOOOOooo E
0-10-0Ten-Wheel Switcher OOOOO E1′
0-10-2Union OOOOOo 1′E
2-10-0Decapod oOOOOO 2′E
4-10-0Mastodon ooOOOOO 1′E1′
2-10-2Santa Fe oOOOOOo 1′E2′
2-10-4Texas oOOOOOoo 2′E1′
4-10-2Southern Pacific, Overland ooOOOOOo F
0-12-0Pennsylvania, Twelve-Wheel-Switcher OOOOOO 1′F
2-12-0Centipede oOOOOOO 1′F1′
2-12-2Javanic oOOOOOOo 2′F1′
4-12-2Union Pacific ooOOOOOOo 2′G2′
4-14-4ooOOOOOOOoo
nameless (AA)
0-2-2-0O O B′B
0-4-4-0
nameless (Mallet)OO OO B′B1
0-4-4-2
nameless (Mallet)OO OOo 2′BB2′
4-4-4-4
nameless (Pennsylvania Railroad Duplex)ooOO OOoo 3′BB3′
6-4-4-6oooOO OOooo 2′CB2′
4-6-4-4
nameless (Pennsylvania Railroad Duplex)ooOOO OOoo C′C
0-6-6-0Erie (Mallet) OOO OOO (1′C)C
2-6-6-0
nameless (Mallet)oOOO OOO (1′C)C1′
2-6-6-2Mallet Mogul (SP), Prairie Mallet (ATSF) oOOO OOOo (1′C)C2′
2-6-6-4
nameless (Simple articulated)oOOO OOOoo (2′C)C2′
4-6-6-4
Challenger (Simple articulated)ooOOO OOOoo (1′C)C3′
2-6-6-6Allegheny (Mallet/Simple articulated) oOOO OOOooo D′D
0-8-8-0Angus (Mallet) OOOO OOOO (1′D)D
2-8-8-0Bullmoose (Mallet) oOOOO OOOO (1′D)D1′
2-8-8-2Chesapeake, Mallet consolidation (Mallet) oOOOO OOOOo (1′D)D2′
2-8-8-4Yellowstone (Mallet/Simple articulated) oOOOO OOOOoo (2′D)D1′
4-8-8-2
Cab Forward (Simple articulated)ooOOOO OOOOo (2′D)D2′
4-8-8-4
Big Boy (Simple articulated)ooOOOO OOOOoo (1′E)E1′
2-10-10-2Virginian (Mallet) oOOOOO+OOOOOo (2′C1′)(1′C2′)
4-6-2+2-6-4Double Pacific (Garratt) ooOOOo+oOOOoo (2′C2′)(2′C2′)
4-6-4+4-6-4Double Hudson (Garratt) ooOOOoo+ooOOOoo (2′D)(D2′)
4-8-0+0-8-4Double Mastodon (Garratt) ooOOOO+OOOOoo (2′D1′)(1′D2′)
4-8-2+2-8-4Double Mountain (Garratt) ooOOOOo+oOOOOoo (2′D2′)(2′D2′)
4-8-4+4-8-4Double Northern (Garratt) ooOOOOoo+ooOOOOoo
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^ Colvin, Fred H. The railroad pocket-book: a quick reference cyclopedia of railroad information. New York, Derry-Collard; London, Locomotive Publishing Company (US-UK co-edition). 1906: L‑9.