एवज़ी की जगह इसके अंग्रेजी शब्द को कुछ लोग ट्रांसलिटरेट करके भी चलाते हैं।

I think that one of these equivalents should serve your purpose.

"फिट होने लायक रिप्लेसमेंट पार्ट" - यह विकल्प भले ही शुद्ध हिंदी शब्दों से सज्जित भले न हो, लेकिन आम लोग या मैकेनिक इसे आसानी से समझ जाएँगे।

to fit यहाँ मेरे विचार से उपयुक्तता का संदर्भ लिए हुए है, आकार-प्रकार के हिसाब से सटीक होना

फिट होने लायक प्रतिस्थापन पुर्जे

...

रमेश के वाहन में मरम्‍मत के दौरान सही प्रतिस्‍थापित हिस्‍सों का प्रयोग किया गया है

A spare part, spare, service part, repair part, or replacement part, is an interchangeable part that is kept in an inventory and used for the repair or replacement of failed units. Spare parts are an important feature of logistics engineering and supply chain management, often comprising dedicated spare parts management systems.

https://en.wikipedia.org/wiki/Spare_part

As you say it is a column heading, "to fit" here means "to be put in position" or "to be installed."

fit verb (PUT IN POSITION)
B2 [T] to provide something and put it in the correct position:All the carpets we sell are fitted free.She's been fitted with an artificial leg.

http://dictionary.cambridge.org/dictionary/english/fit

Also,

fit 1
See definition in Oxford Advanced Learner's Dictionary........

2. Install or fix (something) into place: they fitted smoke alarms to their home
MORE EXAMPLE SENTENCES
• Adam, our installer, was fitting some other stuff and left to go on to another job whilst I changed 16 of the handles.
• If not, why didn't you call a local Sky Installation Engineer to fit your dish?
• So he came round, and we positioned it and fitted the great drive-belt.

http://www.oxforddictionaries.com/definition/english/fit

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