I'm a kind of (sort of/type of) engineer

(= That's the nearest I can come to describing my job.)

It's a kind of (sort of/type of) beetle

(= It's a member of a particular class of beetle.)

3.9.4 The uses of 'a/an' to classify people, etc. [> 2.13.1] A/an can be used freely to refer to 'an example of that class'. We can use He's/It's a + name for 'tangible examples': He's a Forsyte; It's a Picasso; It's a Dickens novel. Other examples are: a Brecht play; a Laura Ashley dress; a Shakespeare sonnet; a Smith and Wesson revolver; a Titian; a Wren church, [compare > 3.27.4]

3.9.5 The use of 'a/an' to refer to 'a certain person'

A/an can be used before titles (Mr, Mrs, Miss, etc.) with the sense of 'a certain person whom I don't know':

A Mr Wingate phoned and left a message for you.

A Mrs Tadley is waiting to see you.

The phrase a certain, to refer to people whose identity is not yet known,

is common in fables and folk stories:

Many years ago a certain merchant arrived in Baghdad

3.10 Quantity: the use of 'a/an' to mean 'only one'

The use of 'a/an' with reference to quantity

The most common use of a/an is in the sense of 'only one' when we are not specifying any particular person or thing:

I'd like an apple (i.e. only one; it doesn't matter which) When we express this in the plural, we use some or any [> 5.10]:

I'd like some apples // don't want any apples [compare > 3.28.8]