When Solomon built the Temple in Jerusalem, there were two main pillars at the entrance, which were named "Boaz" and "Jachin" (1 Kings 7:21: 2 Chronicles 3:17).
There are two alleged contradictions regarding their dimensions:
1 Kings 7:15
15 For he cast two pillars of brass, of eighteen cubits high apiece: and a line of twelve cubits did compass either of them about.
2 Chronicles 3:15
15 Also he made before the house two pillars of thirty and five cubits high, and the chapiter that was on the top of each of them was five cubits.
References to the pillars in 1 Kings 7:15: 2 Kings 25:17, and Jeremiah 52:21 all state that the height of the pillars was 18 cubits.
However, the reference in 2 Chronicles 3:15 says that the pillars were 35 cubits.
The first possibility is that the pillars were more precisely 17.5 cubits each, and the Chronicles account is referring to the height of both of them combined, which would be 35 cubits. The pillars were cast in pieces, with presumably a base, the "pillar" part itself, the chapiter, and a piece that looked like a lilly, being combined to constitute the entire pillar.
The second possibility is that the pillar (18 cubits), the chapiter (5 cubits), the lilly (4 cubits - 1 Kings 7:19), and the base (presumably, 8 cubits) were 35 cubits total, and the chronicler gave the total height first.
1 Kings 7:16
16 And he made two chapiters of molten brass, to set upon the tops of the pillars: the height of the one chapiter was five cubits, and the height of the other chapiter was five cubits:
2 Kings 25:17
17 The height of the one pillar was eighteen cubits, and the chapiter upon it was brass: and the height of the chapiter three cubits; and the wreathen work, and pomegranates upon the chapiter round about, all of brass: and like unto these had the second pillar with wreathen work.
References to the chapiters in 1 Kings 7:15: 2 Kings 25:17, and Jeremiah 52:21 all state that the height of the chapiters was 5 cubits.
However, in 2 Kings 25:17, the height of the chapiters is given as 3 cubits.
This could be due to the fact that the chapiters were capped with pommels (2 Chronicles 4:12), and also two rows of brass pomegranates (2 Chronicles 4:13: 1 Kings 7:20, Jeremiah 52:22). So, in this case, the proper chapiters were 3 cubits, whereas the piece that they constituted was 5 cubits total, and is referred to as a whole in the other accounts.
It could also be that the chapiter was broken/caved in, as the account in 2 Kings 25:1-21 is describing the destruction of the temple by Nebuchadnezzar. The other accounts, then, would be giving the original dimensions, as described in the construction passages.