敲門磚 [－门砖]

Jyutping haau1 mun4 zyun1
Pinyin qiāo mén zhuān

Definitions (CC-CEDICT)

lit. a brick as a door knocker (idiom); fig. a temporary expedient
to use sb as a stepping stone to fortune

Definitions (粵典–words.hk)

名詞
謀求名利嘅手段
stepping stone to fortune; literally: brick as a door knocker

Definitions (Wiktionary)

noun
stepping stone to success

Definitions (Kaifangcidian)

（沒有對應漢語詞彙）