钢筋

Pinyin: gāng jīn
Meaning：Reinforcing steel bar; steel rod
Sentence: 混凝土墙是用钢筋加固的。The concrete walls are reinforced with steel rods.

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钢：

Pinyin: gāng
Meaning: Steel
Radical: 钅
Stokes: 9
Traditional: 鋼
Common words/Phrase:
钢铁 [gāng tiě] 【steel】
钢管 [gāng guǎn] 【steel tube】
钢板 [gāng bǎn] 【armor plate】
钢材 [gāng cái] 【raw steel material】
钢筋 [gāng jīn] 【reinforcing steel bar】

筋：

Pinyin: jīn
Meaning: Muscle; tendon; web
Radical: 竹
Stokes: 12
Traditional: 筋
Common words/Phrase:
筋骨 [jīn gǔ] 【bones and muscles】
筋肉 [jīn ròu] 【brawn】
筋斗 [jīn dǒu] 【flip】
筋络 [jīn luò] 【grain】
筋疲力尽 [jīn pí lì jìn] 【be used up; knock up】